Fix: left-shift operator is breaking highlight in Rust mode

[mkslanc]

Issue #, if available: rust-lang/rust-playground#1061

Description of changes:

After changes:

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Pull Request Checklist:

• No backwards incompatible changes were made to Ace's public interface which is defined through the main typings file (ace.d.ts) and its references:
  • https://github.com/ajaxorg/ace/blob/master/ace.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-modes.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-extensions.d.ts

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.78%. Comparing base (a3277ea) to head (2feadfe).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5572   +/-   ##
=======================================
  Coverage   86.78%   86.78%           
=======================================
  Files         594      594           
  Lines       43017    43017           
  Branches     7129     7129           
=======================================
  Hits        37331    37331           
  Misses       5686     5686           

Flag	Coverage Δ
unittests	86.78% <ø> (ø)

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