Updated the composer.json to require PHP 7.2, removed Travis CI tests for all PHP versions prior to 7.2 and replace jimdo/prometheus_client_php with endclothing/prometheus_client_php to support PHP 7.2.

.travis.yml

@@ -1,11 +1,9 @@
 language: php
 
 php:
-  - 5.6
-  - 7.0
-  - 7.1
   - 7.2
   - 7.3
+  - 7.4
 
 before_install:
   - echo "extension = redis.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini