Warn on invalid semver

[crazy-max]

Closes #20

[codecov]

Codecov Report

Merging #22 (1813dce) into master (ef12c77) will decrease coverage by 0.22%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #22      +/-   ##
==========================================
- Coverage   73.17%   72.94%   -0.23%     
==========================================
  Files           3        3              
  Lines          82       85       +3     
  Branches       17       18       +1     
==========================================
+ Hits           60       62       +2     
  Misses          6        6              
- Partials       16       17       +1     

Impacted Files	Coverage Δ
src/meta.ts	74.60% <66.66%> (-0.40%)	⬇️

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