Enable PHP 7.1 testing on Travis CI

Author: asgrim

.travis.yml

@@ -46,6 +46,16 @@ matrix:
     - php: 7
       env:
         - DEPS=latest
+    - php: 7.1
+      env:
+        - DEPS=lowest
+    - php: 7.1
+      env:
+        - DEPS=locked
+        - CHECK_CS=true
+    - php: 7.1
+      env:
+        - DEPS=latest
     - php: hhvm
       env:
         - DEPS=lowest