Fixes required version of illuminate/encryption

Laravel components doesn’t follow Semantic Versioning. Good article about that: https://medium.com/@vinkla/laravel-packages-and-semantic-versioning-f62dc5accee5

Author: nunomaduro

composer.json

@@ -17,7 +17,7 @@
     ],
     "require": {
         "php": "^7.1",
-        "illuminate/encryption": "~5.6"
+        "illuminate/encryption": "5.6.*"
     },
     "require-dev": {
         "phpunit/phpunit": "^7.0",