chore: bump version to v3.1.0-post (#5884)

Co-authored-by: Alex Rudenko <alexrudenko@chromium.org>

docs/api.md

@@ -1,5 +1,5 @@
 
-# Puppeteer API <!-- GEN:version -->v3.1.0<!-- GEN:stop-->
+# Puppeteer API <!-- GEN:version -->Tip-Of-Tree<!-- GEN:stop-->
 <!-- GEN:empty-if-release --><!-- GEN:stop -->
 
 - Interactive Documentation: https://pptr.dev

package.json

@@ -1,6 +1,6 @@
 {
   "name": "puppeteer",
-  "version": "3.1.0",
+  "version": "3.1.0-post",
   "description": "A high-level API to control headless Chrome over the DevTools Protocol",
   "main": "index.js",
   "repository": "github:puppeteer/puppeteer",