Fix incorrect Typescript types (#62)

Author: henrinormak

index.d.ts

@@ -1,4 +1,3 @@
-declare module 'react-fast-compare' {
-  const isEqual: (a: any, b: any) => boolean
-  export default isEqual
-}
+declare function isEqual(a: any, b: any): boolean;
+declare namespace isEqual {}
+export = isEqual;