Add the push_if_no_changes keyword argument

[DilumAluthge]

Fixes #13

This pull request adds the push_if_no_changes::Bool keyword argument to the bump_stdlibs function.

The default value is push_if_no_changes = false.

[codecov]

Codecov Report

Merging #27 (88f0d86) into master (81111dc) will increase coverage by 7.02%.
The diff coverage is 72.22%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
+ Coverage   85.47%   92.50%   +7.02%     
==========================================
  Files          10       10              
  Lines         303      307       +4     
==========================================
+ Hits          259      284      +25     
+ Misses         44       23      -21     

Impacted Files	Coverage Δ
src/types.jl	100.00% <ø> (ø)
src/inputs.jl	47.05% <44.44%> (-2.95%)	⬇️
src/bump-stdlibs.jl	95.52% <100.00%> (+0.24%)	⬆️
src/git.jl	100.00% <100.00%> (ø)
src/github.jl	88.88% <0.00%> (+43.05%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 81111dc...88f0d86. Read the comment docs.