add memcache tests to travis

.travis.yml

@@ -14,6 +14,7 @@ services:
   
 before_script:
     - if [ ${TRAVIS_PHP_VERSION:0:3} != "5.2" ]; then travis_retry composer --prefer-source --dev install; fi
+    - if [ ${TRAVIS_PHP_VERSION:0:3} <= "5.6" ]; then config-add travis.ini; fi
     - mysql -e "create database IF NOT EXISTS test;" -uroot
 
 install:

travis.ini

@@ -0,0 +1,2 @@
+extension = "memcache.so"
+extension = "apc.so"