not respecting server capabilities ( report-status )

[skadefro]

If server does NOT send report-status. isomorphic-git correctly also leave it out when doing a request.
But still fails with

Expected "unpack ok" or "unpack [error message]" but received "".

at

isomorphic-git/src/wire/parseReceivePackResponse.js

Line 21 in 79a38e0

throw new ParseError('unpack ok" or "unpack [error message]', line)

This check should be skipped when not using report-status

[jcubic]

I'm not sure, but if you can create failing test that pass when the code if fixed. I'm happy to merge your PR.