skipping apc for php 5.5 on travis

tests/unit/data/travis/apc-setup.sh

-echo "extension = apc.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
-echo "apc.enable_cli = 1" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
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+#!/bin/sh
+
+if [ "$(expr "$TRAVIS_PHP_VERSION" "<" "5.5")" -eq 1 ]; then
+	echo "extension = apc.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
+	echo "apc.enable_cli = 1" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
+else
+	echo "Not installing APC as it is not available in PHP 5.5 anymore."
+fi
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