Build: Support jquery-release --dry-run flag

Without this change passing `--dry-run` to jquery-release still pushes to the
jquery-dist repository which is dangerous as one can assume `--dry-run` to be
safe from external side effects.

Close gh-4498

Author: mgol

build/release/dist.js

@@ -130,7 +130,8 @@ module.exports = function( Release, files, complete ) {
 		Release.chdir( Release.dir.dist );
 
 		console.log( "Pushing release to dist repo..." );
-		Release.exec( "git push " + distRemote + " master --tags",
+		Release.exec( "git push " + ( Release.isTest ? " --dry-run " : "" ) +
+			distRemote + " master --tags",
 			"Error pushing master and tags to git repo." );
 
 		// Set repo for npm publish