updatenotification: only notify mm-repo for master if tag present

[khassel]

see discussion here: #2991 (comment)

I still see a need for updating master in special cases (e.g. correct errors in README.md which would otherwise be present up to 3 month until next release) so with this PR only for MagicMirror repo and only for master branch updatenotifications are only triggered if at least one of the new commits has a tag.

May @MichMich must decide if this is wanted.

[codecov-commenter]

Codecov Report

Merging #3004 (04366fb) into develop (877f8ad) will increase coverage by 0.29%.
The diff coverage is 86.48%.

@@             Coverage Diff             @@
##           develop    #3004      +/-   ##
===========================================
+ Coverage    21.94%   22.23%   +0.29%     
===========================================
  Files           51       51              
  Lines        11297    11324      +27     
===========================================
+ Hits          2479     2518      +39     
+ Misses        8818     8806      -12     

Impacted Files	Coverage Δ
...s/default/updatenotification/updatenotification.js	0.00% <0.00%> (ø)
modules/default/updatenotification/git_helper.js	89.58% <87.87%> (-0.84%)	⬇️
modules/default/updatenotification/node_helper.js	90.27% <100.00%> (+23.13%)	⬆️

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[MichMich]

Looks good to me! 👍🏻

[rejas]

If it looks good for @MichMich then it looks good for me too :-)