Fix parsing of multi-line strings in YAML blocks

[dato]

Closes #111.

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[codecov-io]

Codecov Report

Merging #112 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #112   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines          599       600    +1     
=========================================
+ Hits           599       600    +1     

Impacted Files	Coverage Δ
tap/parser.py	100.00% <100.00%> (ø)

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[mblayman]

Thanks for the contribution and finding this issue. The fix looks good to me. 👍