Test against PHP 7.1, 7.2, and 7.3 on TravisCI

Author: WyriHaximus

.travis.yml

@@ -5,7 +5,10 @@ php:
   - 5.4
   - 5.5
   - 5.6
-  - 7
+  - 7.0
+  - 7.1
+  - 7.2
+  - 7.3
   - hhvm # ignore errors, see below
 
 # lock distro so new future defaults will not break the build