Fix sourcing and scripts' permissions

[mjbogusz]

I’ve ran into 2 minor issues, however both prevented the plugin from working whatsoever.

One was that the source_vars.sh script became unexecutable (maybe Package Control did something? I sure didn’t).

Other was that the aforementioned script uses source [another-script] in an /bin/sh context, which is invalid on platforms where sh != bash (I think most Linux distros work that way, I’ve observed this behaviour on Ubuntu).

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A simple patch for both issues included (git apply fix.patch in main project dir should do the trick).

I’m not able to create a pull request because Bitbucket is being Bitbucket and it was unable to even fork the repo in the last 30 minutes, let alone let me clone/push to my fork. Have you considered switching platforms to something more reliable and user-friendly, like git{hub,lab}?