Fix TypeScript definition (#138)

Author: LitoMore

index.d.ts

@@ -45,7 +45,7 @@ export interface ColorSupport {
 
 export type ColorInfo = ColorSupport | false;
 
-export function createSupportsColor(stream: WriteStream, options?: Options): ColorInfo;
+export function createSupportsColor(stream?: WriteStream, options?: Options): ColorInfo;
 
 declare const supportsColor: {
 	stdout: ColorInfo;

index.test-d.ts

@@ -9,5 +9,6 @@ expectType<ColorInfo>(supportsColor.stderr);
 
 expectType<ColorInfo>(createSupportsColor(stdout));
 expectType<ColorInfo>(createSupportsColor(stderr));
+expectType<ColorInfo>(createSupportsColor(undefined));
 
 expectType<ColorInfo>(createSupportsColor(stdout, options));