Replace travis with Github Actions

[codecov[bot]]

Codecov Report

Merging #77 (c916e66) into master (45b70f5) will decrease coverage by 25.50%. The diff coverage is 40.93%.

@@             Coverage Diff             @@
##           master      #77       +/-   ##
===========================================
- Coverage   97.10%   71.60%   -25.51%     
===========================================
  Files           5        4        -1     
  Lines         173      324      +151     
===========================================
+ Hits          168      232       +64     
- Misses          5       92       +87     

Impacted Files	Coverage Δ
src/ParticleDistributions/ParticleDistributions.jl	59.64% <38.46%> (-36.95%)	:arrow_down:
src/Sources/Sources.jl	97.50% <100.00%> (+0.53%)	:arrow_up:
src/Kernels/KernelFunctions.jl	100.00% <0.00%> (ø)
src/Cloudy.jl
src/Kernels/KernelTensors.jl	98.30% <0.00%> (+0.30%)	:arrow_up:

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[charleskawczynski]

bors r+

[bors[bot]]

Build succeeded:

• ci 1.7.2 - macOS-latest
• ci 1.7.2 - ubuntu-latest
• ci 1.7.2 - windows-latest
• docbuild