Fix iTerm shell integration

[andreiborisov]

Fixes #116

[edouard-lopez]

Thanks,
could you add a tests/fish_mode_prompt.test.fish that assert:

• $status is 0
• output is empty

[andreiborisov]

@edouard-lopez I have no idea why tests are failing, can you look into that?

[edouard-lopez]

@schrodincat

fish_mode_prompt doesn't print any so there is no string to compare,
but we can check the output has no length.

But I think there are problems with other tests.

[andreiborisov]

fish_mode_prompt doesn't print any so there is no string to compare, but we can check the output has no length

Yep, I came to the same conclusion.