Drop support for php 5.4 and 5.5

Add travis for php 7.1
Changed symfony version to 2.7 and 3.2

Author: cmodijk

.travis.yml

@@ -3,27 +3,16 @@ language: php
 sudo: false
 
 php:
-  - 5.4
-  - 5.5
   - 5.6
   - 7.0
+  - 7.1
 
 matrix:
   include:
-    - php: 5.6
-      env: SYMFONY_VERSION="2.3.*"
-    - php: 5.6
-      env: SYMFONY_VERSION="2.4.*"
-    - php: 5.6
-      env: SYMFONY_VERSION="2.5.*"
-    - php: 5.6
-      env: SYMFONY_VERSION="2.6.*"
-    - php: 5.6
+    - php: 7.1
       env: SYMFONY_VERSION="2.7.*"
-    - php: 5.6
-      env: SYMFONY_VERSION="2.8.*@dev"
-    - php: 5.6
-      env: SYMFONY_VERSION="3.0.*@dev"
+    - php: 7.1
+      env: SYMFONY_VERSION="3.2.*"
 
 before_install:
   - composer self-update

composer.json

@@ -17,7 +17,7 @@
         }
     ],
     "require": {
-        "php": ">=5.4",
+        "php": ">=5.6",
         "simple-bus/message-bus": "~2.0",
         "symfony/http-kernel": "~2.3|~3.0",
         "symfony/dependency-injection": "~2.3|~3.0",