fix #4 - update generator to support autocompleting kafka commands that end with ".sh"

[atsu85]

resolves #4

This PR makes autocomplete work also when hitting tab after
kafka-console-producer.sh --

that developers may want to use when command name itself is autocompleted based on file name present in the OS $PATH

not only after
kafka-console-producer --
that was supported previously

[atsu85]

Note that others have tried to work around the same issue with different approaches:

• @AndreaTosti only updated the generated file with this commit, not the generator itself as in this PR
• @bioker added a workaround instructions with this commit that made copies of all kafka sh scripts without sh extension, so that OS would suggest command names without ".sh" extension when command is in OS $PATH