fix(package): update styled-components to version 4.2.1

Closes #106

Author: greenkeeper[bot]

package.json

@@ -71,7 +71,7 @@
     "react-apollo": "^2.1.3",
     "react-dom": "^16.3.1",
     "react-ga": "^2.4.1",
-    "styled-components": "^3.2.5",
+    "styled-components": "^4.2.1",
     "styled-system": "^3.0.0"
   },
   "devDependencies": {