it seems on MSWindows MSYS bash, echo n puts a literal \n (not a newline) into the commit message, so lets get more primitive

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge pull request #4419 from SvenDowideit/tweak-DCO-hook-for-windows

Fix newlines echoing in DCO git hook contrib script