Fix GAP coverage script newline issue

[reiniscirpons]

This PR fixes the GAP coverage script on certain platforms. The issue seems to be caused by feeding raw \n newlines into gap, as a fix we add non-raw newlines after the _GAP_COMMANDS are created.

Once accepted, these changes should also be propagated to the Digraphs package, since it uses an identical script.

[reiniscirpons]

As an aside, what is the --open parameter used for in the script? I thought it was a flag which would open the overall coverage index.html my browser, but it seems like it takes a file and outputs a link to the specific coverage for that file (with a specific reference to a missing line if the coverage contains a missed line).

[james-d-mitchell]

Thanks @reiniscirpons