Fix regression in hg patch

Review Request #11330 — Created Dec. 14, 2020 and submitted — Latest diff uploaded

Information

RBTools
master
dc6bf66...

Reviewers

Review request 11279 moved to using buffered standard output which broke
`rbt land` for mercurial.  This simple fix accounts for that.

Ran the unit tests (had 2 failures regarding svn not being installed) and successfully landed a review request with mercurial.