Regression with Docs parsing

[etorreborre]

Describe and demonstrate the bug The following Doc fails to typecheck with ucm 0.5.26:

testDoc : Doc
testDoc = {{
  key: '{{ s "value" }}'.
}}

The error is:

I got confused here:
  
      3 |   key: '{{ s "value" }}'.
  
  
  I was surprised to find a . here.
  I was expecting one of these instead:
  
  * end of input

The same code typechecks ok with 0.5.25.