Add support for publishing a package that isn't at repo root

Author: adrw

README.md

@@ -8,6 +8,15 @@ you'll need to configured that workflow yourself. You can look to the
 
 ### Workflow
 
+* Set `PACKAGE_PATH` env variable if `package.json` is not in repo root directory
+  ```
+  - name: Publish
+      uses: mikeal/merge-release@master
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        NPM_AUTH_TOKEN: ${{ secrets.NPM_AUTH_TOKEN }}
+        PACKAGE_PATH: ./packages/my-package
+  ```
 * Check for the latest version number published to npm.
 * Lookup all commits between the git commit that triggered the action and the latest publish.
   * If the package hasn't been published or the prior publish does not include a git hash, we'll

merge-release-run.js

@@ -12,7 +12,7 @@ const get = bent('json', 'https://registry.npmjs.org/')
 
 const event = JSON.parse(fs.readFileSync('/github/workflow/event.json').toString())
 
-let pkg = require(path.join(process.cwd(), 'package.json'))
+let pkg = require(path.join(process.env.PACKAGE_PATH || process.cwd(), 'package.json'))
 
 const run = async () => {
   if (!process.env.NPM_AUTH_TOKEN) throw new Error('Merge-release requires NPM_AUTH_TOKEN')