update travis config for 5.5 target

Author: michaeldyrynda

.travis.yml

@@ -6,14 +6,8 @@ cache:
 
 matrix:
   include:
-    - php: 5.6.4
-      env: ILLUMINATE_VERSION=5.4.*
-    - php: 7.0
-      env: ILLUMINATE_VERSION=5.4.*
     - php: 7.0
       env: ILLUMINATE_VERSION=5.5.*
-    - php: 7.1
-      env: ILLUMINATE_VERSION=5.4.*
     - php: 7.1
       env: ILLUMINATE_VERSION=5.5.*