Pull and clone with `--depth 1`.

This greatly reduces bandwidth by not retrieving the entire tree.
In theory, this would break Vim plugins that assume they're git repos
and use the tree, but in practice I've never seen this.

autoload/vundle/installer.vim

@@ -407,7 +407,7 @@ func! s:make_sync_command(bang, bundle) abort
 
     let cmd_parts = [
                 \ 'cd '.vundle#installer#shellesc(a:bundle.path()),
-                \ 'git pull',
+                \ 'git pull --depth 1',
                 \ 'git submodule update --init --recursive',
                 \ ]
     let cmd = join(cmd_parts, ' && ')
@@ -415,7 +415,7 @@ func! s:make_sync_command(bang, bundle) abort
 
     let initial_sha = s:get_current_sha(a:bundle)
   else
-    let cmd = 'git clone --recursive '.vundle#installer#shellesc(a:bundle.uri).' '.vundle#installer#shellesc(a:bundle.path())
+    let cmd = 'git clone --recursive --depth 1 '.vundle#installer#shellesc(a:bundle.uri).' '.vundle#installer#shellesc(a:bundle.path())
     let initial_sha = ''
   endif
   return [cmd, initial_sha]