remove fixed dependancy

Author: Minishlink

composer.json

@@ -12,21 +12,14 @@
       "homepage": "https://github.com/Minishlink"
     }
   ],
-  "repositories": [
-    {
-      "type": "vcs",
-      "url": "https://github.com/Minishlink/PHPASN1"
-    }
-  ],
   "require": {
     "php": "^5.6 || ^7.0",
     "mdanter/ecc": "^0.4.0",
     "lib-openssl": "*",
     "spomky-labs/base64url": "^1.0",
     "spomky-labs/php-aes-gcm": "^1.2",
     "spomky-labs/jose": "^6.0",
-    "guzzlehttp/guzzle": "^6.2",
-    "fgrosse/phpasn1": "dev-fix_mbstring_overload as 1.5.2"
+    "guzzlehttp/guzzle": "^6.2"
   },
   "require-dev": {
     "phpunit/phpunit": "4.8.*"