fix(eslint-plugin): [require-await] crash when await is used outside of async

[a-tarasyuk]

Fixes #1077

[typescript-eslint]

Thanks for the PR, @a-tarasyuk!

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The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[codecov]

Codecov Report

Merging #1212 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1212      +/-   ##
==========================================
+ Coverage   94.15%   94.15%   +<.01%     
==========================================
  Files         124      124              
  Lines        5334     5337       +3     
  Branches     1491     1492       +1     
==========================================
+ Hits         5022     5025       +3     
  Misses        178      178              
  Partials      134      134

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/require-await.ts	93.18% <100%> (+0.49%)	⬆️

[bradzacher]

See: #1077 (comment)