Fixed a bug in the release name generation

[ansasaki]

Prefixes containing "-" should not be accepted. Added a fix to replace the invalid "-" character for a valid "_" character.

[codecov-io]

Codecov Report

Merging #68 into master will increase coverage by <.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #68      +/-   ##
==========================================
+ Coverage   96.58%   96.59%   +<.01%     
==========================================
  Files           4        4              
  Lines         733      734       +1     
  Branches      186      186              
==========================================
+ Hits          708      709       +1     
  Misses          6        6              
  Partials       19       19

Impacted Files	Coverage Δ
src/smap/symver.py	96.53% <100%> (ø)	:arrow_up:

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[coveralls]

Pull Request Test Coverage Report for Build 122

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 97.842%

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Totals
Change from base Build 118:	0.002%
Covered Lines:	728
Relevant Lines:	734

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💛 - Coveralls