Drop Laravel 5.5 support

Author: Omranic

composer.json

@@ -39,13 +39,13 @@
     ],
     "require": {
         "php": "^7.1.3",
-        "illuminate/auth": "~5.5.0|~5.6.0",
-        "illuminate/bus": "~5.5.0|~5.6.0",
-        "illuminate/contracts": "~5.5.0|~5.6.0",
-        "illuminate/http": "~5.5.0|~5.6.0",
-        "illuminate/routing": "~5.5.0|~5.6.0",
-        "illuminate/support": "~5.5.0|~5.6.0",
-        "illuminate/validation": "~5.5.0|~5.6.0"
+        "illuminate/auth": "~5.6.0",
+        "illuminate/bus": "~5.6.0",
+        "illuminate/contracts": "~5.6.0",
+        "illuminate/http": "~5.6.0",
+        "illuminate/routing": "~5.6.0",
+        "illuminate/support": "~5.6.0",
+        "illuminate/validation": "~5.6.0"
     },
     "require-dev": {
         "codedungeon/phpunit-result-printer": "^0.6.0",