macos+vim+plug.vim, 为什么不加载～/.vim/autoload/文件夹下的 plug.vim 文件呢

有大佬遇到过这样的问题吗，之前一直在 Windows 上使用这样的配置，没有出现过任何问题， 不过 Windows 上是放在$VIM/vimfiles/autoload/下的，我看了 plug.vim 的官网，unix 上面也是放在～/.vim/autoload/文件夹下 vim 就会自动加载。

启动 vi m 的时候， 提示 Plug not a command, 这就是没加载到 plug.vim 文件？

VIM - Vi IMproved 8.0 (2016 Sep 12, compiled Sep 29 2017 00:58:02) MacOS X (unix) version Included patches: 1-1150 Compiled by Homebrew Huge version without GUI. Features included (+) or not (-): +acl +cmdline_hist -ebcdic -gettext +listcmds +mouse_sgr +persistent_undo +smartindent +termresponse +wildignore +arabic +cmdline_info +emacs_tags -hangul_input +localmap -mouse_sysmouse +postscript +startuptime +textobjects +wildmenu +autocmd +comments +eval +iconv -lua +mouse_urxvt +printer +statusline +timers +windows -balloon_eval +conceal +ex_extra +insert_expand +menu +mouse_xterm +profile -sun_workshop +title +writebackup -browse +cryptv +extra_search +job +mksession +multi_byte -python +syntax -toolbar -X11 ++builtin_terms +cscope +farsi +jumplist +modify_fname +multi_lang +python3 +tag_binary +user_commands -xfontset +byte_offset +cursorbind +file_in_path +keymap +mouse -mzscheme +quickfix +tag_old_static +vertsplit -xim +channel +cursorshape +find_in_path +lambda -mouseshape +netbeans_intg +reltime -tag_any_white +virtualedit -xpm +cindent +dialog_con +float +langmap +mouse_dec +num64 +rightleft -tcl +visual -xsmp -clientserver +diff +folding +libcall -mouse_gpm +packages +ruby +termguicolors +visualextra -xterm_clipboard +clipboard +digraphs -footer +linebreak -mouse_jsbterm +path_extra +scrollbind +terminal +viminfo -xterm_save +cmdline_compl -dnd +fork() +lispindent +mouse_netterm +perl +signs +terminfo +vreplace system vimrc file: "$VIM/vimrc" user vimrc file: "$HOME/.vimrc" 2nd user vimrc file: "~/.vim/vimrc" user exrc file: "$HOME/.exrc" defaults file: "$VIMRUNTIME/defaults.vim" fall-back for $VIM: "/usr/local/share/vim"