Merge pull request #138 from WyriHaximus-secret-labs/travis-7.3

Test against PHP 7.3 on travis

Author: jsor

.travis.yml

@@ -9,6 +9,7 @@ php:
 # - 7.0 # Mac OS X test setup, ignore errors, see below
   - 7.1
   - 7.2
+  - 7.3
   - nightly # ignore errors, see below
   - hhvm # ignore errors, see below