Pin memcache version to PHP7 supported version.

To fix the build.

Author: Ian Jenkins

.travis.yml

@@ -16,13 +16,15 @@ before_install:
     - sudo apt-get install zlib1g-dev
     - pecl channel-update pecl.php.net
     - pecl config-set preferred_state beta
-    - echo 'yes' | pecl install memcache
+    - echo 'yes' | pecl install memcache-4.0.5.2
     - echo "extension = memcache.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
+    - phpenv config-rm xdebug.ini
 
 install:
     - composer update --prefer-dist --prefer-stable
 
 before_script:
+    - phpenv config-rm xdebug.ini
     - memcached -p 11212 -d
     - "./bin/install-wp-tests.sh wordpress_test root '' localhost $WP_VERSION"
     - export COMPOSER_BIN_DIR="$HOME/.config/composer/vendor/bin"