Update: no-extra-parens supports async/await (refs #7101)

[mysticatea]

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update
[x] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Tell us about your environment

• ESLint Version: master
• Node Version: 6.3.0
• npm Version: 3.8.9

What parser (default, Babel-ESLint, etc.) are you using?

• default

Please show your full configuration:

• nothing

What did you do? Please include the actual source code causing the issue.

A:

$ echo "async function a() { await (a); }" | eslint --stdin --no-eslintrc --parser-options "ecmaVersion:8" --rule "no-extra-parens:error"

B:

$ echo "async function a() { (await a)(); }" | eslint --stdin --no-eslintrc --parser-options "ecmaVersion:8" --rule "no-extra-parens:error"

What did you expect to happen?

In the case A, it should show an error: "Gratuitous parentheses around expression no-extra-parens".
In the case B, it should not show errors.

What actually happened? Please include the actual, raw output from ESLint.

In the case A, it did not show the error.
In the case B, it showed the following errors:

<text>
  1:22  error  Gratuitous parentheses around expression  no-extra-parens

✖ 1 problem (1 error, 0 warnings)

Please check each item to ensure your pull request is ready:

• I've read the pull request guide
• I've included tests for my change
• I've updated documentation for my change (if appropriate)

What changes did you make? (Give an overview)

This PR adds the supports of await expressions into no-extra-parens.
The precedence of await expression is same as unary expressions: https://tc39.github.io/ecmascript-asyncawait/#UnaryExpression

Semver-minor: this is a bug fix which increases errors.

Is there anything you'd like reviewers to focus on?

Nothing in particular.

Refs #7101.

[eslintbot]

LGTM

[platinumazure]

LGTM, but would like another set of eyes on this.

[nzakas]

Lgtm, just waiting another day.