Update CLI code link in README

Author: kevinbarabash

README.md

@@ -20,7 +20,7 @@ afterwards, e.g. changing `SyntheticEvent` to `React.Event`.
 - `yarn global add @khanacademy/flow-to-ts`
 - `flow-to-ts [options] <file globs>`
 
-For a comprehensive list of available options, please check out the [CLI code](./src/cli.js).
+For a comprehensive list of available options, please check out the [CLI code](./src/cli.ts).
 
 # Playground