Bump terser from 4.8.0 to 5.2.1

[dependabot-preview]

Bumps terser from 4.8.0 to 5.2.1.

Changelog

Sourced from terser's changelog.

v5.2.1

• The parse step now doesn't accept an ecma option, so that all ES code is accepted.
• Optional dotted chains now accept keywords, just like dotted expressions (foo?.default)

v5.2.0

• Optional chaining syntax is now supported.
• Consecutive await expressions don't have unnecessary parens
• Taking the variable name's length (after mangling) into consideration when deciding to inline

v5.1.0

• import.meta is now supported
• Typescript typings have been improved

v5.0.0

• in operator now taken into account during property mangle.
• Fixed infinite loop in face of a reference loop in some situations.
• Kept exports and imports around even if there's something which will throw before them.
• The main exported bundle for commonjs, dist/bundle.min.js is no longer minified.

v5.0.0-beta.0

• BREAKING: minify() is now async and rejects a promise instead of returning an error.
• BREAKING: Internal AST is no longer exposed, so that it can be improved without releasing breaking changes.
• BREAKING: Lowest supported node version is 10
• BREAKING: There are no more warnings being emitted
• Module is now distributed as a dual package - You can import and require() too.
• Inline improvements were made

Commits

• 4e3ca5d 5.2.1
• f3fedac update changelog
• 4bcb2cf accept keywords as optional properties (closes #796); disable ecma option whe...
• e0c1a2b 5.2.0
• 3e0e59e update changelog
• 7aad3cb initial implementation of optional chaining (a?.b?.(c))
• 23abbc3 remove some unused code, assume mangled variables have length 1
• b573cda take variable name length into consideration before inlining.
• 82be4b4 remove unnecessary parens in consecutive awaits.
• 9dc2dcd Add module to package.json (#784)
• Additional commits viewable in compare view

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[coveralls]

Coverage increased (+0.08%) to 92.856% when pulling c0044b7 on dependabot/npm_and_yarn/terser-5.2.1 into 95ac50f on master.

[RandomByte]

Changes look good 🚀

[matz3]

"Internal" or "Feature"?
We can now process new language features like Optional chaining in the uglify task, but our bundler which uses esprima still can't handle it.
So at the end not really something worth mentioning as a feature update, so I would just go for "Internal".

[RandomByte]

Either internal or [DEPENDENCY] (which also appears in the changelog)