Update php-http/message dependency to ^1.0

Author: lanthaler

composer.json

@@ -19,7 +19,7 @@
  "phpunit/phpunit": "^4.5",
  "php-http/httplug": "^1.0",
  "php-http/discovery": "~0.7",
- "php-http/message": "~0.2.1",
+ "php-http/message": "^1.0",
  "guzzlehttp/psr7": "^1.0",
  "th3n3rd/cartesian-product": "^0.3"
  },