Make php-http/message hard dependency, fixes #28

Author: sagikazarmark

composer.json

@@ -16,10 +16,10 @@
         "php-http/message-factory": "^1.0",
         "php-http/promise": "^0.1.1",
         "php-http/client-common": "^0.1.1",
+        "php-http/message": "^0.1.1",
         "symfony/options-resolver": "^2.6|^3.0"
     },
     "require-dev": {
-        "php-http/message": "^0.1.1",
         "php-http/cookie": "^0.1@dev",
         "symfony/stopwatch": "^2.3",
         "psr/log": "^1.0",
@@ -38,7 +38,6 @@
         }
     },
     "suggest": {
-        "php-http/message": "Allow to use Authentication and Encoding plugins",
         "php-http/cookie": "Allow to use CookiePlugin",
         "symfony/stopwatch": "Allow to use the StopwatchPlugin",
         "psr/log-implementation": "Allow to use the LoggerPlugin",