Use git -C for setting working dir

It is way better to tell git which dir to use instead of actually changing the current directory.
Use git clone --local instead of -l

Short command line options are meant to be typed.
Only long ones should be used in code to be easily understood.
Use composer --working-dir

Similar to git -C it better to tell Composer which working directory to use
instead of actually changing the working directory.

Another small nit is that the `--dev` option is now the default.
It may be removed in the future.
Use `--no-dev` if you want only the `require` section to be used.
Merge pull request #7 from lox/working-dir

Set working dir instead of changing it