Added memcached service in Travis YAML

.travis.yml

@@ -10,6 +10,7 @@ env:
 
 services:
   - redis-server
+  - memcached
 
 before_script:
   - composer self-update && composer --version
@@ -24,4 +25,4 @@ script:
   - phpunit --coverage-clover tests/unit/runtime/coveralls/clover.xml --verbose --exclude-group mssql,oci,wincache,xcache,zenddata
 
 after_script:
-  - php vendor/bin/coveralls
\ No newline at end of file
+  - php vendor/bin/coveralls