Merge branch 'update-dependencies'

Closes #9

Author: akrabat

.travis.yml

@@ -3,9 +3,15 @@ sudo: false
 language: php
 
 php:
-  - 5.5
-  - 5.6
   - 7.0
+  - 7.1
+  - 7.2
+  - nightly
+
+matrix:
+  allow_failures:
+    - php: nightly
+
 
 before_install:
   - composer self-update

composer.json

@@ -18,7 +18,8 @@
         "psr/http-message": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8",
+        "php": ">=7.0",
+        "phpunit/phpunit": "^6",
         "squizlabs/php_codesniffer": "^2.3",
         "zendframework/zend-diactoros": "^1.1"
     },