Add react/react-dom as devDependencies

packages/gatsby-plugin-netlify-cms/package.json

@@ -17,7 +17,9 @@
  "devDependencies": {
  "@babel/cli": "^7.0.0-beta.53",
  "@babel/core": "^7.0.0-beta.53",
- "cross-env": "^5.1.3"
+ "cross-env": "^5.1.3",
+ "react": "^16.4.1",
+ "react-dom": "^16.4.1"
  },
  "homepage": "https://github.com/gatsbyjs/gatsby/tree/master/packages/gatsby-plugin-netlify-cms#readme",
  "keywords": [

yarn.lock

@@ -6496,7 +6496,7 @@ fb-watchman@^2.0.0:
  dependencies:
  bser "^2.0.0"
 
-fbjs@^0.8.14:
+fbjs@^0.8.14, fbjs@^0.8.16:
  version "0.8.17"
  resolved "https://registry.yarnpkg.com/fbjs/-/fbjs-0.8.17.tgz#c4d598ead6949112653d6588b01a5cdcd9f90fdd"
  dependencies:
@@ -12557,6 +12557,15 @@ react-docgen@3.0.0-beta12:
  node-dir "^0.1.10"
  recast "^0.13.0"
 
+react-dom@^16.4.1:
+ version "16.4.1"
+ resolved "https://registry.yarnpkg.com/react-dom/-/react-dom-16.4.1.tgz#7f8b0223b3a5fbe205116c56deb85de32685dad6"
+ dependencies:
+ fbjs "^0.8.16"
+ loose-envify "^1.1.0"
+ object-assign "^4.1.1"
+ prop-types "^15.6.0"
+
 react-error-overlay@^3.0.0:
  version "3.0.0"
  resolved "https://registry.yarnpkg.com/react-error-overlay/-/react-error-overlay-3.0.0.tgz#c2bc8f4d91f1375b3dad6d75265d51cd5eeaf655"
@@ -12599,6 +12608,15 @@ react-router@^4.1.1, react-router@^4.3.1:
  prop-types "^15.6.1"
  warning "^4.0.1"
 
+react@^16.4.1:
+ version "16.4.1"
+ resolved "https://registry.yarnpkg.com/react/-/react-16.4.1.tgz#de51ba5764b5dbcd1f9079037b862bd26b82fe32"
+ dependencies:
+ fbjs "^0.8.16"
+ loose-envify "^1.1.0"
+ object-assign "^4.1.1"
+ prop-types "^15.6.0"
+
 read-all-stream@^3.0.0:
  version "3.1.0"
  resolved "https://registry.yarnpkg.com/read-all-stream/-/read-all-stream-3.1.0.tgz#35c3e177f2078ef789ee4bfafa4373074eaef4fa"