Upgrade react + related deps; upgrade react-styleguidist

* Upgrades react/react-dom from 16.4.2 => 16.12.0.
  * Also upgrades any deps that rely on certain versions of
    react like enzyme/react-test-renderer
* Upgrades react-styleguidist from 9 => 10. This was the original
  target package to upgrade since it had the outdated
  serialize-javascript dependency
* Sets an explicit version of node in package.json
* Updates circleci config to use node 10 (required by the newer
  version of react-styleguidist)

.circleci/config.yml

@@ -2,7 +2,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: circleci/node:8.11.4
+      - image: circleci/node:10
 
     working_directory: ~/repo
 

package.json

@@ -3,6 +3,9 @@
   "version": "0.0.143",
   "description": "The Instacart Component Library for Web",
   "main": "dist/snacks.js",
+  "engines": {
+    "node": ">=10.0.0 <11.0.0"
+  },
   "module": "dist/esm/index.js",
   "types": "dist/esm/index.d.ts",
   "scripts": {
@@ -64,7 +67,7 @@
     "coveralls": "^3.0.5",
     "enzyme": "^3.10.0",
     "enzyme-adapter-react-16": "^1.15.1",
-    "enzyme-to-json": "^3.3.3",
+    "enzyme-to-json": "^3.4.3",
     "eslint": "6.2.2",
     "eslint-import-resolver-webpack": "0.11.0",
     "fs-extra": "^5.0.0",
@@ -73,10 +76,10 @@
     "prettier": "1.16.4",
     "prompt": "^1.0.0",
     "radium": "^0.22.0",
-    "react": "16.4.2",
-    "react-dom": "16.4.2",
-    "react-styleguidist": "9.0.9",
-    "react-test-renderer": "16.4.2",
+    "react": "^16.12.0",
+    "react-dom": "^16.12.0",
+    "react-styleguidist": "^10.2.1",
+    "react-test-renderer": "^16.12.0",
     "react-transition-group": "^2.2.1",
     "sinon": "^7.3.2",
     "terser-webpack-plugin": "^2.3.2",