not support markdown file

hi, i am using VIM8 in ubuntu. while i use UpdateTags to update the tags for a Markdown file, it hits errors below. Can you please fix it?

```
:UpdateTags

easytags.vim 3.11: Exuberant Ctags doesn't support the 'markdown' file type! (at function xolox#easytags#update[6]..<SNR>43_check_cfile，line  22)

```