ci: Move to GitHub actions

[ankitpokhrel]

Travis is effectively shutting down open source support.

[codecov]

Codecov Report

Merging #342 (7d0885f) into master (d044ac9) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #342      +/-   ##
============================================
- Coverage     99.68%   99.68%   -0.01%     
  Complexity      356      356              
============================================
  Files            20       20              
  Lines           957      952       -5     
============================================
- Hits            954      949       -5     
  Misses            3        3              

Impacted Files	Coverage Δ	Complexity Δ
src/Response.php	100.00% <0.00%> (ø)	11.00% <0.00%> (ø%)
src/Tus/Server.php	100.00% <0.00%> (ø)	92.00% <0.00%> (ø%)
src/Middleware/GlobalHeaders.php	100.00% <0.00%> (ø)	1.00% <0.00%> (ø%)

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