build: update babel-preset-gatsby and sass (#798)

Author: koba04

www/package.json

@@ -14,7 +14,7 @@
   "license": "MIT",
   "dependencies": {
     "@babel/core": "^7.3.4",
-    "babel-preset-gatsby": "^0.1.8",
+    "babel-preset-gatsby": "^2.7.0",
     "bootstrap": "^4.3.1",
     "gatsby": "^2.1.22",
     "gatsby-plugin-react-helmet": "^3.0.10",
@@ -28,10 +28,10 @@
     "react": "^16.8.3",
     "react-bootstrap": "^1.0.0-beta.5",
     "react-dom": "^16.8.3",
-    "react-helmet": "^5.2.0"
+    "react-helmet": "^5.2.0",
+    "sass": "^1.49.7"
   },
   "devDependencies": {
-    "gh-pages": "^2.0.1",
-    "node-sass": "^4.12.0"
+    "gh-pages": "^2.0.1"
   }
 }