Tests: Add the 3.x-git jQuery version to the dropdown

Closes jquerygh-1905

Author: mgol

tests/lib/qunit.js

@@ -34,7 +34,7 @@ QUnit.config.urlConfig.push( {
 		"3.2.0", "3.2.1",
 		"3.3.0", "3.3.1",
 		"3.4.0", "3.4.1",
-		"git", "custom"
+		"3.x-git", "git", "custom"
 	],
 	tooltip: "Which jQuery Core version to test against"
 } );