fix: do not break selector with escaping

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Fix escaping in selectors

fixes #578

Breaking Changes

No

Additional Info

/cc @jquense Looks like all tests good, except some selectors we need fix before merge

postcss/postcss-selector-parser#174
postcss/postcss-selector-parser#175

[codecov]

Codecov Report

Merging #896 into master will decrease coverage by 0.24%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master     #896      +/-   ##
==========================================
- Coverage   99.47%   99.23%   -0.25%     
==========================================
  Files          10       10              
  Lines         381      391      +10     
  Branches      109      114       +5     
==========================================
+ Hits          379      388       +9     
- Misses          2        3       +1

Impacted Files	Coverage Δ
src/utils.js	97.22% <90.9%> (-2.78%)	⬇️

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[alexander-akait]

Awesome!

[alexander-akait]

ID selectors still broken, WIP on this

[alexander-akait]

Problem in postcss-selector-parser
Invalid parse (should has one ID selector, but contains two):

:local(#\#fake-id) { 
  color: red; 
}

https://codepen.io/anon/pen/qvNzja?&editable=true (example with not)