fix(typescript-estree): parsing error for await in non-async func

[kaicataldo]

Fixes #987

This PR adds a parsing error for when await is used in a non-async function, which matches both espree and babel-eslint's behavior. Is this something the rest of the team agrees should be done? Is this the correct way to solve this?

[typescript-eslint]

Thanks for the PR, @kaicataldo!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

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 #988 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #988   +/-   ##
=======================================
  Coverage   94.13%   94.13%           
=======================================
  Files         115      115           
  Lines        5016     5016           
  Branches     1403     1403           
=======================================
  Hits         4722     4722           
  Misses        166      166           
  Partials      128      128

Impacted Files	Coverage Δ
...escript-estree/src/semantic-or-syntactic-errors.ts	87.5% <ø> (ø)
packages/typescript-estree/src/parser.ts	93.05% <100%> (ø)	⬆️