fix: follow html specs with regards to end tags

[pimlie]

While I was looking at the changes done by the html-minifier when generating my (Nuxt) project, I noticed that vue-meta doesnt strictly follow the html specifications. Both base, link as meta tags dont need to have an endtag. See: https://www.w3.org/TR/html52/document-metadata.html

Fixes: #270

[codecov-io]

Codecov Report

Merging #314 into master will decrease coverage by 0.15%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #314      +/-   ##
==========================================
- Coverage   41.04%   40.89%   -0.16%     
==========================================
  Files          19       19              
  Lines         268      269       +1     
==========================================
  Hits          110      110              
- Misses        158      159       +1

Impacted Files	Coverage Δ
src/server/generators/tagGenerator.js	0% <0%> (ø)	⬆️

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[TheAlexLichter]

Thank you ☺️