Bumps minimum node engine to 8+ (#4474)

* Use node 8 as development environment

* fixup! Use node 8 as development environment

* bump node to 8.10

* Targets node 8 for everything

* Run npm install so lock file is up to date

* Use push adapter v3

* Deflake a test on ParseUser

* Adds slight delay after logout

* Ensure we wait even if call fails

* Use node carbon

.babelrc

@@ -6,7 +6,7 @@
     "presets": [
         ["env", {
             "targets": {
-                "node": "6.11.4"
+                "node": "8"
             }
         }]
     ]