Only test on Redis 4.3.0 for now

PhpRedis 5.0.0 was released with some breaking changes which we'll need to fix first before we can run builds on it.

Author: driesvints

Diff for: .travis.yml

@@ -30,7 +30,7 @@ services:
 before_install:
   - phpenv config-rm xdebug.ini || true
   - echo "extension = memcached.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
-  - printf "\n" | pecl install -f redis
+  - printf "\n" | pecl install -f redis-4.3.0
   - travis_retry composer self-update
   - mysql -e 'CREATE DATABASE forge;'