Incorrect parsing of Flow annotations with generics inside JSX

[mroch]

let foo = <bar x={function(x): Array<string> {}} />;

fails to parse (as of babylon-6.7.0: astexplorer), saying the / is unexpected.

wrapping Array<string> in parens parses correctly.

[sebmck]

Found it, due to some weird context issues with identifying whether { is a statement or expression.