Make this client adapter compatible with PSR18. (php-http#51)

* Make this client adapter compatible with PSR18.

* Show provide

* Add return type hint

* syntax

* Better deps

* Update composer.json

* Update integration test package version

* bump branch alias to 2.x

* "psr/http-client": "^1.0",

composer.json

@@ -16,16 +16,18 @@
     ],
     "require": {
         "php": "^7.1",
-        "php-http/httplug": "^1.0",
+        "php-http/httplug": "^2.0",
+        "psr/http-client": "^1.0",
         "guzzlehttp/guzzle": "^6.0"
     },
     "require-dev": {
         "ext-curl": "*",
-        "php-http/client-integration-tests": "^0.6"
+        "php-http/client-integration-tests": "^2.0"
     },
     "provide": {
         "php-http/client-implementation": "1.0",
-        "php-http/async-client-implementation": "1.0"
+        "php-http/async-client-implementation": "1.0",
+        "psr/http-client-implementation": "1.0"
     },
     "autoload": {
         "psr-4": {
@@ -43,7 +45,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "1.2-dev"
+            "dev-master": "2.x-dev"
         }
     }
 }

src/Client.php

@@ -9,6 +9,7 @@
 use Http\Client\HttpAsyncClient;
 use Http\Client\HttpClient;
 use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * HTTP Adapter for Guzzle 6.
@@ -49,7 +50,7 @@ public static function createWithConfig(array $config)
     /**
      * {@inheritdoc}
      */
-    public function sendRequest(RequestInterface $request)
+    public function sendRequest(RequestInterface $request): ResponseInterface
     {
         $promise = $this->sendAsyncRequest($request);