Update semver.md

In the other part of the document the word 'SemVer' is used. I think it is a good idea to use same word in the document.
Merge pull request #140 from bessarabov/patch-1

Update semver.md
Fix wrapping of overlength line in Summary section
Merge pull request #142 from wincent/wrap-fix

Fix wrapping of overlength line in Summary section