Revert "Update TravisCI configuration"

This reverts commit 80fd1b6.

Author: sebastianbergmann

.travis.yml

@@ -3,35 +3,27 @@ language: php
 php:
   - 5.6
   - 7.0
-  - 7.0snapshot
   - 7.1
-  - 7.1snapshot
-  - master
+  - nightly
+
+env:
+  matrix:
+    - DRIVER="xdebug"
+    - DRIVER="phpdbg"
 
 matrix:
-  allow_failures:
-    - php: master
-  fast_finish: true
   exclude:
     - php: 5.6
       env: DRIVER="phpdbg"
 
-env:
-  matrix:
-    - DRIVER="xdebug" DEPENDENCIES="high"
-    - DRIVER="phpdbg" DEPENDENCIES="high"
-    - DRIVER="xdebug" DEPENDENCIES="low"
-    - DRIVER="phpdbg" DEPENDENCIES="low"
-
 sudo: false
 
 before_install:
   - composer self-update
   - composer clear-cache
 
 install:
-  - if [[ "$DEPENDENCIES" = 'high' ]]; then travis_retry composer update --no-interaction --no-ansi --no-progress --no-suggest --optimize-autoloader --prefer-stable; fi
-  - if [[ "$DEPENDENCIES" = 'low' ]]; then travis_retry composer update --no-interaction --no-ansi --no-progress --no-suggest --optimize-autoloader --prefer-stable --prefer-lowest; fi
+  - travis_retry composer update --no-interaction --no-ansi --no-progress --no-suggest --optimize-autoloader --prefer-stable
 
 script:
   - if [[ "$DRIVER" = 'phpdbg' ]]; then phpdbg -qrr vendor/bin/phpunit; fi