chore: fix typo api.json (#565) [ci skip]

Author: zyy7259

.github/contributing.md

@@ -112,7 +112,7 @@ The `--types` flag will generate type declarations during the build and in addit
 
 - Roll the declarations into a single `.dts` file for each package;
 - Generate an API report in `<projectRoot>/temp/<packageName>.api.md`. This report contains potential warnings emitted by [api-extractor](https://api-extractor.com/).
-- Generate an API model json in `<projectRoot>/temp/<packageName>.api.md`. This file can be used to generate a Markdown version of the exported APIs.
+- Generate an API model json in `<projectRoot>/temp/<packageName>.api.json`. This file can be used to generate a Markdown version of the exported APIs.
 
 ### `yarn dev`