Remove version alias for "dev-master"

I don't know whether the next version will be a MINOR or a MAJOR
version, therefore it makes no sense to keep an alias for "dev-master".

Signed-off-by: Henrique Moody <[email protected]>

Author: henriquemoody

composer.json

@@ -52,11 +52,6 @@
             "Respect\\Validation\\Test\\": "tests/library/"
         }
     },
-    "extra": {
-        "branch-alias": {
-            "dev-master": "2.0-dev"
-        }
-    },
     "scripts": {
         "docheader": "vendor/bin/docheader check library/ tests/",
         "phpcs": "vendor/bin/phpcs",