knife-spork: git plugin improvements

We should be able to push to the branch the user is currently on instead of master by default.

This will allow users to use the branch they are on instead of a hard-coded branch that is the same for each push.

lib/knife-spork/plugins/git.rb

@@ -177,12 +177,6 @@ def after_promote_local
           git_add(environment_path,"#{environment}.json")
         end
         if config.auto_push
-          branch =  if not config.branch.nil?
-                      config[:branch] 
-                    else 
-                      "master"
-                    end
-
           git_commit(environment_path, "promote #{cookbooks.collect{ |c| "#{c.name}@#{c.version}" }.join(",")} to #{environments.join(",")}")
           git_push(branch)
         end
@@ -380,7 +374,7 @@ def remote
       end
 
       def branch
-        config.branch || 'master'
+        config.branch || `git rev-parse --abbrev-ref HEAD`
       end
 
       def tag_name