Add compatibility to L5.3 + add some tests (#8)

* Update deps

* refactored service provider

* Add service provider tests

* small fixes

Author: ptondereau

composer.json

@@ -11,11 +11,13 @@
   ],
   "require": {
     "php": ">=7.0",
-    "illuminate/support": "^5.2",
-    "illuminate/http": "^5.2"
+    "illuminate/contracts": "5.1.*|5.2.*|5.3.*",
+    "illuminate/support": "5.1.*|5.2.*|5.3.*",
+    "illuminate/http": "5.1.*|5.2.*|5.3.*"
   },
   "require-dev": {
-    "phpunit/phpunit": "^5.4"
+    "phpunit/phpunit": "^5.4",
+    "graham-campbell/testbench": "^3.1"
   },
   "autoload": {
     "psr-4": {