Missing hyphen in git-http-backend

Add missing hyphen in the command name.
One more...
Add missing hyphen

The command is git diff --check.
Merge pull request #140 from paveljanik/patch-3

Missing hyphen in git-http-backend
Merge pull request #141 from paveljanik/patch-4

Add missing hyphen
Fix some typos

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>