Allow httplug 2.0

Author: acrobat

composer.json

@@ -20,16 +20,16 @@
         "php": "^5.6 || ^7.0",
         "psr/http-message": "^1.0",
         "psr/cache": "^1.0",
-        "php-http/httplug": "^1.1",
+        "php-http/httplug": "^1.1 || ^2.0",
         "php-http/discovery": "^1.0",
         "php-http/client-implementation": "^1.0",
-        "php-http/client-common": "^1.6",
+        "php-http/client-common": "^1.6 || ^2.0",
         "php-http/cache-plugin": "^1.4"
     },
     "require-dev": {
         "phpunit/phpunit": "^5.5 || ^6.0",
-        "php-http/guzzle6-adapter": "^1.0",
-        "php-http/mock-client": "^1.0",
+        "php-http/guzzle6-adapter": "^1.0 || ^2.0",
+        "php-http/mock-client": "^1.2",
         "guzzlehttp/psr7": "^1.2",
         "cache/array-adapter": "^0.4"
     },