do not sync when `sync` is set to `no`

autoload/vundle/config.vim

@@ -81,8 +81,12 @@ endf
 
 let s:bundle = {}
 
+func! s:bundle.nosync() 
+  return has_key(self, 'sync') && 'no' == self.sync()
+endf
+
 func! s:bundle.path()
-  if has_key(self, 'sync') && 'no' == self.sync
+  if self.nosync()
     if isdirectory(expand(self.uri))
       let path = expand(self.uri)
     endif

autoload/vundle/installer.vim

@@ -62,6 +62,7 @@ func! s:helptags(rtp) abort
 endf
 
 func! s:sync(bang, bundle) abort
+  if a:bundle.nosync() | return 0 | endif
   let git_dir = expand(a:bundle.path().'/.git')
   if isdirectory(git_dir)
     if !(a:bang) | return 0 | endif