fix typing to make outputPath actually accept null (#395)

* Update index.tsx

change signature to match the docs  / java/ objc code that say null is allowed to use the cache directory

* Update NativeImageResizer.ts

change types

Author: 1mike12

src/NativeImageResizer.ts

@@ -11,7 +11,7 @@ export interface Spec extends TurboModule {
     mode: string,
     onlyScaleDown: boolean,
     rotation?: number,
-    outputPath?: string,
+    outputPath?: string | null,
     keepMeta?: boolean
   ): Promise<{
     path: string;

src/index.tsx

@@ -21,7 +21,7 @@ function createResizedImage(
   format: ResizeFormat,
   quality: number,
   rotation: number = 0,
-  outputPath?: string,
+  outputPath?: string | null,
   keepMeta = false,
   options: Options = defaultOptions
 ): Promise<Response> {