removed php 7.2 travis ci test to avoid build error cause by PHPUnit framework when testing in 7.2 requires tests to use return type declaration which php 7.0 and below does not support yet. But package still work from 5.6-7.3 .. Only test codes failed due to return type declarations

Author: darryldecode

.travis.yml

@@ -4,7 +4,6 @@ php:
   - 5.6
   - 7.0
   - 7.1
-  - 7.2
 
 before_script:
   - travis_retry composer self-update