Always use git.ruby-lang.org as origin

naruse sets remote.origin.pushUrl = nonexistent as fail-safe
configuration to avoid accidentally push a new branch to origin.

tool/merger.rb

@@ -12,6 +12,7 @@ require 'uri'
 require 'shellwords'
 
 ENV['LC_ALL'] = 'C'
+ORIGIN = 'git@git.ruby-lang.org:ruby.git'
 
 module Merger
   REPOS = 'svn+ssh://svn@ci.ruby-lang.org/ruby/'
@@ -150,7 +151,7 @@ class << Merger
       unless execute('git', 'tag', tagname)
         abort 'specfied tag already exists. check tag name and remove it if you want to force re-tagging'
       end
-      execute('git', 'push', 'origin', tagname, interactive: true)
+      execute('git', 'push', ORIGIN, tagname, interactive: true)
     end
   end
 
@@ -176,7 +177,7 @@ class << Merger
       execute('svn', 'rm', '-m', "remove tag #{tagname}", tag_url, interactive: true)
     else
       execute('git', 'tag', '-d', tagname)
-      execute('git', 'push', 'origin', ":#{tagname}", interactive: true)
+      execute('git', 'push', ORIGIN, ":#{tagname}", interactive: true)
     end
   end
 
@@ -218,7 +219,7 @@ class << Merger
       current_branch = IO.popen(['git', 'rev-parse', '--abbrev-ref', 'HEAD'], &:read).strip
       execute('git', 'add', '.') &&
         execute('git', 'commit', '-F', file) &&
-        execute('git', 'push', 'origin', current_branch)
+        execute('git', 'push', ORIGIN, current_branch)
     end
   end