Add *.lexs to ftdetect for Temple templates

[rktjmp]

Adds support for Temple templates.

They are just elixir code, so all that is needed is to match the extra extension: *.lexs (*.exs is already covered obviously).

[mhanberg]

Just saw this!

In the mean time, I have this in my init.lua config autocmd([[BufRead,BufNewFile *.lexs set filetype=elixir]])

(i'm the author of temple)

[jbodah]

LGTM thanks