Use `gsed` for compatibility of `sed` on OSX

Command line tools for those coming from a unix
backgroud often have issues ensuring things just work
I've run into multiple issues of such kind using sed
on OSX. That's which I discovered gnu-sed
. As I understand it, it the version of sed
that runs in OSX and is compatible with the unix
version commands.
Installation is simple:
brew install gnu-sed
It gets installed at /usr/local/bin/gsed
Fire up gsed
as use it as you would normally do in a unix
environment. Everything seems to work as expected for now!