Fix: include all src files when running yarn coverage

[Laityned]

Why am I submitting this PR

#583

Does it fix an existing ticket?

Yes #583

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• tests are included and pass: yarn test (see details here)
• documentation is changed or added

[codecov-commenter]

Codecov Report

Merging #586 (b3ccef8) into master (cc29d02) will increase coverage by 95.32%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #586       +/-   ##
===========================================
+ Coverage        0   95.32%   +95.32%     
===========================================
  Files           0       11       +11     
  Lines           0     1624     +1624     
===========================================
+ Hits            0     1548     +1548     
- Misses          0       76       +76     

Impacted Files	Coverage Δ
src/parser.js	100.00% <0.00%> (ø)
src/lexers/jsx-lexer.js	98.06% <0.00%> (ø)
src/lexers/base-lexer.js	96.29% <0.00%> (ø)
src/lexers/html-lexer.js	100.00% <0.00%> (ø)
src/lexers/vue-lexer.js	100.00% <0.00%> (ø)
src/helpers.js	100.00% <0.00%> (ø)
src/lexers/javascript-lexer.js	96.48% <0.00%> (ø)
src/index.js	100.00% <0.00%> (ø)
src/transform.js	88.30% <0.00%> (ø)
src/lexers/handlebars-lexer.js	100.00% <0.00%> (ø)
... and 1 more

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[karellm]

Thanks!