Fix spread attribute

[ezhlobo]

Issue: #101

The real fix is upgrading pug-lexer to the upper version.

I also added some tests in order not to overlook that case accidentally.

[codecov-io]

Codecov Report

Merging #102 into master will increase coverage by 0.21%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
+ Coverage   86.92%   87.14%   +0.21%     
==========================================
  Files          21       21              
  Lines         459      459              
  Branches      112      112              
==========================================
+ Hits          399      400       +1     
+ Misses         54       53       -1     
  Partials        6        6

Impacted Files	Coverage Δ
src/visitors/Tag.js	88.52% <0%> (+1.63%)	⬆️

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