Test against PHP 7.3 on travis

WyriHaximus · WyriHaximus · commit df184588d493 · 2018-10-26T17:31:27.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -8,6 +8,7 @@ php:
   - 7.0
   - 7.1
   - 7.2
+  - 7.3
 # - 7.0 # Mac OS X, ignore errors, see below
   - hhvm # ignore errors, see below
 
