Fix shiftwidth=0 being ignored

[neocryses]

Quoting from vim's 'options.txt' documentation, shiftwidth is:

  Number of spaces to use for each step of (auto)indent.  Used for
  |'cindent'|, |>>|, |<<|, etc.
  When zero the 'ts' value will be used.  Use the |shiftwidth()|
  function to get the effective shiftwidth value.

Which means if I have shiftwidth=0 and tabstop=2 in $MYVIMRC, shiftwidth should fallback to being set to 2, and auto indentation using = should indent with 2 spaces.

However with the minimal rc below, auto indenting an html file with gg=G removes all the indents. (Meaning every line will be at indentation level 0 after gg=G.)

filetype plugin indent on
syntax enable

" Using vim-plug as the plugin manager
call plug#begin('~/.vim/plugged/')
Plug  'othree/html5.vim'
call plug#end()

set shiftwidth=0
sed tabstop=2

This PR will fix that up.