v0.125.0

Likely to cause new Flow errors:

• Fixed signatures generated in types-first for classes with non-trivial expressions
  in their extends clauses, which were before treated like extending any.

New features:

• Types-first is no longer an experimental mode, but is now fully supported!

Notable bug fixes:

• Fixed a soundness bug that allowed refined property expressions to be treated as
  empty in some circumstances.

Misc:

• Added $FlowIssue and $FlowExpectedError as default suppression comments.
• Improved quality of AST and comment printing and layout.
• Improved quality of type printing for type-at-pos and friends.
• Added '.cjs' to default extensions list.

Parser:

• Fixed ranges of sequence and assignment expressions that contain grouping parentheses.
• Disallowed newline after type keyword in type aliases.

Library definitions:

• Added headers timeout to http & https server (thanks, @mattconde!)
• Added flushHeaders to http$ServerResponse (thanks, @gajus!)
• Changed thisArg parameter for array callback functions (e.g. map, reduce) to mixed.
• Added more precise typing for common cases of Array.flat.