remove PHP 7.2 from allowed failures and handle master like all 7 versions

(to fix missing PHP Unit)

.travis.yml

@@ -9,7 +9,6 @@ php:
 matrix:
   fast_finish: true
   allow_failures:
-    - php: 7.2
     - php: master
 
 services:
@@ -34,7 +33,7 @@ before_script:
        phpenv config-rm xdebug.ini;
        composer require 'phpunit/phpunit:~5.7';
        ;;
-    "7"|"7.0"|"7.1"|"7.2"|"7.3")
+    "7"|"7.0"|"7.1"|"7.2"|"7.3"|"master")
        yes "" | pecl install apcu;
        echo "extension=memcached.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini;
        phpenv config-rm xdebug.ini;