deps: Update lua client
Merge PR #1616 'Update lua client'
shell: Fix shell command output

Shell command output was broken in @8a5a8db, which refactored nvim to no longer
switch to cooked mode(linefeeds are processed differently).

Fix the problem by refactoring write_output to accept to extra arguments that
control the flushing behavior and where data will be written to: buffer or
directly to the screen.