neovim: Allow filename completion after `=`
neovim: Allow filename completion after `=`

By default, `=` is treated as a character which may appear in a
filename, which prevents filename completion after an equals sign. For
example, the following completion of a variable assignment does not
work:

    export HOME_PATH=/home/<CTRL-X><CTRL-F>

This commit removes `=` as a recognised character for filenames to
enable this.

srstevenson/dotfiles,srstevenson/dotfiles,srstevenson/dotfiles