travis: revert stages, shorten feedback loop

.travis.yml

@@ -1,6 +1,7 @@
 language: php
 
 php:
+  - 7.2
   - 7.1
 
 install:
@@ -8,10 +9,7 @@ install:
 
 script:
   - vendor/bin/phpunit --coverage-clover coverage.xml
-  # disable xdebug
   - phpenv config-rm xdebug.ini || return 0
-  # check coding standard (defined in composer.json "scripts" section)
-  # if this fails, run "composer fix-cs" to fix all fixable issues
   - composer check-cs
 
 after_script:
@@ -19,5 +17,9 @@ after_script:
   - wget https://github.com/satooshi/php-coveralls/releases/download/v1.0.1/coveralls.phar
   - php coveralls.phar --verbose
 
+cache:
+  directories:
+    - $HOME/.composer/cache
+
 notifications:
   email: never