Add more PHP Versions to travis

Author: LKaemmerling

.travis.yml

@@ -12,9 +12,11 @@ php:
   # aliased to a recent 7.x version
   - 7.1
   - 7.2
+  - 7.3 
+  - 7.4snapshot
   - nightly
 
 services:
   - docker
 
-script: vendor/bin/paratest -p8 tests
+script: vendor/bin/paratest -p8 tests