Upgrade acorn to version 7.1.1

[depfu]

Here is everything you need to know about this upgrade. Please take a good look at what changed and the test results before merging this pull request.

What changed?

✳️ acorn (^6.1.1 → ^7.1.1) · Repo

Commits

See the full diff on Github. The new version differs by 20 commits:

• Mark release 7.1.1
• More rigorously check surrogate pairs in regexp validator
• Fix incorrect comment in regexp parser
• Parameterize dummy value and export `isDummy`
• Further refine acorn-walk types
• Fix some errors in walk types
• Mark acorn-walk 7.1.1
• Further clean up walker types
• Remove NarrowNode from walk.d.ts
• Fix: acorn-walk type work with acorn's
• Mark acorn-walk 7.1.0
• Do not reset shorthandAssign when parsing maybeAssign
• fix: triple __proto__ in patterns should not throw
• types added
• Allow exponential op in await expression
• types property added to package.json
• disallow non octal like in BigInt literals
• allow escape sequence in IdentifierName
• update test262
• Treat \8 and \9 as invalid escapes in template strings

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[depfu]

Closed in favor of #56.