`wl-copy` by default tries to determine the mime type of a copied bit of
text. From the [readme](https://github.com/bugaevc/wl-clipboard):
> wl-copy automatically infers the type of the copied content by running
> xdg-mime(1) on it.
So copying a Ruby script from Nvim may store it in the Wayland clipboard
as mime-type `application/x-ruby`.
This is a small reproduction without Nvim:
$ cat test.rb
#!/usr/bin/env ruby
puts 'hello world'
$ cat test.rb | wl-copy
$ wl-paste --list-types
application/x-ruby
This commit fixes that by telling wl-copy that all text copied from
Nvim has the mime type `text/plain`.
$ cat test.rb | wl-copy --type text/plain
$ wl-paste --list-types
text/plain;charset=utf-8
d8316f2a1b
