Update GitHub token regex in sample config

[jwodder]

The format of GitHub tokens changed back in April. This PR updates the regex given in the sample config to match, based on the information here and here.

[codecov-commenter]

Codecov Report

Merging #108 (083d7a4) into master (d724f18) will increase coverage by 27.67%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #108       +/-   ##
===========================================
+ Coverage   44.45%   72.12%   +27.67%     
===========================================
  Files           9       10        +1     
  Lines         893      897        +4     
  Branches      134      134               
===========================================
+ Hits          397      647      +250     
+ Misses        495      197      -298     
- Partials        1       53       +52     

Impacted Files	Coverage Δ
src/tinuous/_version.py	100.00% <0.00%> (ø)
src/tinuous/util.py	86.36% <0.00%> (+6.81%)	⬆️
src/tinuous/config.py	92.63% <0.00%> (+18.94%)	⬆️
src/tinuous/github.py	51.00% <0.00%> (+20.50%)	⬆️
src/tinuous/base.py	88.09% <0.00%> (+26.19%)	⬆️
src/tinuous/travis.py	63.63% <0.00%> (+35.45%)	⬆️
src/tinuous/appveyor.py	76.19% <0.00%> (+44.04%)	⬆️
src/tinuous/__main__.py	55.38% <0.00%> (+55.38%)	⬆️

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[yarikoptic]

Interesting, I have managed to miss/not spot the change -- it is good news though since makes it easier to avoid false positives. Thank you!