Remove 5.5, 5.6, 7.0, add 7.2, 7.3

Author: carlbennett

.travis.yml

@@ -4,11 +4,8 @@ os:
   - linux
 sudo: false
 php:
-# - 5.3 (doesn't recognize $var=[], only recognizes $var=array())
-# - 5.4 (doesn't have finally{} in try blocks)
-  - 5.5
-  - 5.6
-  - 7.0
+  - 7.2
+  - 7.3
   - nightly
 matrix:
   allow_failures: