Keep parens around type assertion if in binexp

[JohnnyMorganz]

Fix #441

[codecov]

Codecov Report

Merging #443 (fdd5b20) into master (602d1a2) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #443      +/-   ##
==========================================
+ Coverage   96.42%   96.44%   +0.01%     
==========================================
  Files          14       14              
  Lines        5228     5257      +29     
==========================================
+ Hits         5041     5070      +29     
  Misses        187      187              

Impacted Files	Coverage Δ
src/formatters/expression.rs	97.04% <100.00%> (+0.12%)	⬆️

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