Build(deps-dev): bump babel-preset-gatsby from 0.2.18 to 0.2.20 (#4216)

Bumps [babel-preset-gatsby](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/babel-preset-gatsby) from 0.2.18 to 0.2.20.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/babel-preset-gatsby/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/babel-preset-gatsby@0.2.20/packages/babel-preset-gatsby)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package-lock.json

@@ -4132,9 +4132,9 @@
       }
     },
     "babel-preset-gatsby": {
-      "version": "0.2.18",
-      "resolved": "https://registry.npmjs.org/babel-preset-gatsby/-/babel-preset-gatsby-0.2.18.tgz",
-      "integrity": "sha512-shJDlx0Fgof1mb8jHM1EOgAcf/k7utMBiQYp+6me8L5J6DNLjJqfNUoHroqwSZjGLvr7cF0siKF9pxVrQ5J2uA==",
+      "version": "0.2.20",
+      "resolved": "https://registry.npmjs.org/babel-preset-gatsby/-/babel-preset-gatsby-0.2.20.tgz",
+      "integrity": "sha512-vKDeNhszAjTiHpgIyzLOxf9NCY9Jbw7k2yi6m4i9b9uPySCU19b/oRifYA0bC5cRj76vfoicSjykFGuwjj0Tyw==",
       "dev": true,
       "requires": {
         "@babel/plugin-proposal-class-properties": "^7.5.5",

package.json

@@ -166,7 +166,7 @@
     "@typescript-eslint/parser": "^1.13.0",
     "babel-plugin-inline-react-svg": "^1.1.0",
     "babel-plugin-istanbul": "^5.2.0",
-    "babel-preset-gatsby": "^0.2.18",
+    "babel-preset-gatsby": "^0.2.20",
     "caller": "^1.0.1",
     "chai": "^4.1.2",
     "chai-datetime": "^1.5.0",