[JS/Flow] Implicit return values break syntax highlighting when `<` or `>` used in type definitions

[TomasBarry]

When defining methods where the types have a < or a > (Array<...> or any Flow utility type) and that method implicitly returns a value the syntax highlighting breaks down. Take the following simple example:

// @flow

const someMethod = (params: Array<string>): Array<string> => params

console.log('some console')

The syntax highlighting breaks down after the implicit return of `params. However, if the above was defined as:

// @flow

const someMethod = (param: string): string => params

console.log('some console')

The syntax highlighting remains intact.

The first example can be fixed by using the long-form with an explicit return:

// @flow

const someMethod = (params: Array<string>): Array<string> => { return params }

console.log('some console')