feat: lower the engine requirement to node 10.15.0 (microsoft#750)

Some people are still on 10.15, like the Google cloud. We can relax our supported node version a little bit to support them.

package.json

@@ -4,7 +4,7 @@
   "description": "A high-level API to automate web browsers",
   "repository": "github:Microsoft/playwright",
   "engines": {
-    "node": ">=10.17.0"
+    "node": ">=10.15.0"
   },
   "main": "index.js",
   "playwright": {