fixed code blocks in migration docs

docs/guide/migration.md

@@ -28,25 +28,24 @@ Creating Migrations
 
 To create a new migration (e.g. create a news table), we run the following command:
 
-~~~
+```
 yii migrate/create <name>
-~~~
+```
 
 The required `name` parameter specifies a very brief description of the migration
 (e.g. `create_news_table`). As we will show in the following, the `name` parameter
 is used as part of a PHP class name. Therefore, it should only contain letters,
 digits and/or underscore characters.
 
-~~~
+```
 yii migrate/create create_news_table
-~~~
+```
 
 The above command will create under the `protected/migrations` directory a new
 file named `m101129_185401_create_news_table.php` which contains the following
 initial code:
 
-~~~
-[php]
+```php
 class m101129_185401_create_news_table extends \yii\db\Migration
 {
 	public function up()
@@ -59,7 +58,7 @@ class m101129_185401_create_news_table extends \yii\db\Migration
 		return false;
 	}
 }
-~~~
+```
 
 Notice that the class name is the same as the file name which is of the pattern
 `m<timestamp>_<name>`, where `<timestamp>` refers to the UTC timestamp (in the
@@ -78,8 +77,7 @@ method returns `false` to indicate that the migration cannot be reverted.
 
 As an example, let's show the migration about creating a news table.
 
-~~~
-[php]
+```php
 class m101129_185401_create_news_table extends \yii\db\Migration
 {
 	public function up()
@@ -96,7 +94,7 @@ class m101129_185401_create_news_table extends \yii\db\Migration
 		$this->db->createCommand()->dropTable('tbl_news')->execute();
 	}
 }
-~~~
+```
 
 The base class [\yii\db\Migration] exposes a database connection via `db`
 property. You can use it for manipulating data and schema of a database.
@@ -112,8 +110,7 @@ DB transactions.
 We could explicitly start a DB transaction and enclose the rest of the DB-related
 code within the transaction, like the following:
 
-~~~
-[php]
+```php
 class m101129_185401_create_news_table extends \yii\db\Migration
 {
 	public function up()
@@ -138,7 +135,7 @@ class m101129_185401_create_news_table extends \yii\db\Migration
 
 	// ...similar code for down()
 }
-~~~
+```
 
 > Note: Not all DBMS support transactions. And some DB queries cannot be put
 > into a transaction. In this case, you will have to implement `up()` and
@@ -152,9 +149,9 @@ Applying Migrations
 To apply all available new migrations (i.e., make the local database up-to-date),
 run the following command:
 
-~~~
+```
 yii migrate
-~~~
+```
 
 The command will show the list of all new migrations. If you confirm to apply
 the migrations, it will run the `up()` method in every new migration class, one
@@ -169,18 +166,18 @@ application component.
 Sometimes, we may only want to apply one or a few new migrations. We can use the
 following command:
 
-~~~
+```
 yii migrate/up 3
-~~~
+```
 
 This command will apply the 3 new migrations. Changing the value 3 will allow
 us to change the number of migrations to be applied.
 
 We can also migrate the database to a specific version with the following command:
 
-~~~
+```
 yii migrate/to 101129_185401
-~~~
+```
 
 That is, we use the timestamp part of a migration name to specify the version
 that we want to migrate the database to. If there are multiple migrations between
@@ -195,9 +192,9 @@ Reverting Migrations
 To revert the last one or several applied migrations, we can use the following
 command:
 
-~~~
+```
 yii migrate/down [step]
-~~~
+```
 
 where the optional `step` parameter specifies how many migrations to be reverted
 back. It defaults to 1, meaning reverting back the last applied migration.
@@ -212,9 +209,9 @@ Redoing Migrations
 Redoing migrations means first reverting and then applying the specified migrations.
 This can be done with the following command:
 
-~~~
+```
 yii migrate/redo [step]
-~~~
+```
 
 where the optional `step` parameter specifies how many migrations to be redone.
 It defaults to 1, meaning redoing the last migration.
@@ -226,10 +223,10 @@ Showing Migration Information
 Besides applying and reverting migrations, the migration tool can also display
 the migration history and the new migrations to be applied.
 
-~~~
+```
 yii migrate/history [limit]
 yii migrate/new [limit]
-~~~
+```
 
 where the optional parameter `limit` specifies the number of migrations to be
 displayed. If `limit` is not specified, all available migrations will be displayed.
@@ -246,9 +243,9 @@ version without actually applying or reverting the relevant migrations. This
 often happens when developing a new migration. We can use the following command
 to achieve this goal.
 
-~~~
+```
 yii migrate/mark 101129_185401
-~~~
+```
 
 This command is very similar to `yii migrate/to` command, except that it only
 modifies the migration history table to the specified version without applying
@@ -290,17 +287,17 @@ line:
 
 To specify these options, execute the migrate command using the following format
 
-~~~
+```
 yii migrate/up --option1=value1 --option2=value2 ...
-~~~
+```
 
 For example, if we want to migrate for a `forum` module whose migration files
 are located within the module's `migrations` directory, we can use the following
 command:
 
-~~~
+```
 yii migrate/up --migrationPath=ext.forum.migrations
-~~~
+```
 
 
 ### Configure Command Globally