Contract changes

Author: sagikazarmark

composer.json

@@ -15,7 +15,7 @@
         "phpunit/phpunit": "~4.4"
     },
     "require-dev": {
-        "php-http/adapter-core": "dev-initial_import"
+        "php-http/adapter-core": "dev-contract_changes"
     },
     "autoload": {
         "psr-4": {