Small fixes

[ansasaki]

Small changes:

• docs: Use https instead of http
• symver: Replace deprecated method warn() with warning() for logging
• ci: Fixed coverage run options
• tests: Added test case to check that an update without changes does not create the output file

[codecov-io]

Codecov Report

Merging #84 into master will not change coverage. The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #84   +/-   ##
=======================================
  Coverage   97.56%   97.56%           
=======================================
  Files           4        4           
  Lines         740      740           
  Branches      190      190           
=======================================
  Hits          722      722           
  Partials       18       18

Impacted Files	Coverage Δ
src/abimap/symver.py	97.52% <100%> (ø)	:arrow_up:

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[coveralls]

Pull Request Test Coverage Report for Build 173

• 28 of 28 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.489%

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Totals
Change from base Build 169:	0.0%
Covered Lines:	740
Relevant Lines:	740

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💛 - Coveralls