[CLI] Fix package entry point path (#136)

## Motivation for the change, related issues Before this PR, installing `@wp-playground/cli` and importing functions from it would result in a `Error: Failed to resolve entry for package "@wp-playground/cli". The package may have incorrect main/module/exports specified in its package.json.` error. The error is caused by the incorrect primary entry point defined in `package.json`. This PR updates the entry point to `index.js`, which matches the entry point of the built package. ## Testing Instructions (or ideally a Blueprint) - Build Playground CLI - Open `dist/packages/playground/cli/index.js` and confirm it's the primary entry point for the package (it should contain the same export as `packages/playground/cli/src/index.ts`)

Author: bgrgicak

packages/playground/cli/package.json

@@ -21,7 +21,7 @@
 },
 "license": "GPL-2.0-or-later",
 "type": "module",
-"main": "main.js",
+"main": "index.js",
 "bin": "wp-playground.js",
 "gitHead": "2f8d8f3cea548fbd75111e8659a92f601cddc593"
 }