Updated php travis matrix to also test for php nightly

Author: Toflar

.travis.yml

@@ -5,15 +5,19 @@ matrix:
     - php: 5.6
     - php: 5.6
       env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable'
+    - php: 7.0
     - php: 7.0
       env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable'
     - php: 7.1
     - php: 7.1
       env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable'
-      env: COVERAGE='--coverage-clover build/logs/clover.xml'
     - php: 7.2
+      env: COVERAGE='--coverage-clover build/logs/clover.xml'
     - php: 7.2
       env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable'
+    - php: nightly
+    - php: nightly
+      env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable'
   fast_finish: true
 
 sudo: false