' character in types creates invalid TS syntax

[John Jackson]

@gentype
type t' = int

Outputs:

// tslint:disable-next-line:interface-over-type-literal
export type t' = number;

Perhaps it should compile to t$prime, like how the ReScript compiler treats values with ' characters?

[Cristiano Calcagno]

@johnridesabike handled here: #494