Make git clone also grab submodules

With just `git clone`, submodules are not grabbed. This is an issue for
certain plugins, such as 'kevinw/pyflakes-vim' that requires a pyflakes
submodule

autoload/vundle/installer.vim

@@ -216,7 +216,7 @@ func! s:sync(bang, bundle) abort
     let get_current_sha = 'cd '.shellescape(a:bundle.path()).' && git rev-parse HEAD'
     let initial_sha = s:system(get_current_sha)[0:15]
   else
-    let cmd = 'git clone '.a:bundle.uri.' '.shellescape(a:bundle.path())
+    let cmd = 'git clone --recursive '.a:bundle.uri.' '.shellescape(a:bundle.path())
     let initial_sha = ''
   endif