use Shallow Clones instead of complete Clones to speed up the :BundleInstall step

autoload/vundle/installer.vim

@@ -222,7 +222,7 @@ func! s:sync(bang, bundle) abort
     let get_current_sha = g:shellesc_cd(get_current_sha)
     let initial_sha = s:system(get_current_sha)[0:15]
   else
-    let cmd = 'git clone --recursive '.shellescape(a:bundle.uri).' '.shellescape(a:bundle.path())
+    let cmd = 'git clone --dept=1 --recursive '.shellescape(a:bundle.uri).' '.shellescape(a:bundle.path())
     let initial_sha = ''
   endif