move styled-components from devDependencies to dependencies to stop heroku crashing

Author: sima-qian

package.json

@@ -42,7 +42,6 @@
     "node-fetch": "^2.2.0",
     "nodemon": "^1.18.4",
     "react-testing-library": "^5.1.1",
-    "styled-components": "^4.0.2",
     "supertest": "^3.3.0"
   },
   "dependencies": {
@@ -67,6 +66,7 @@
     "react-router": "^4.3.1",
     "react-router-dom": "^4.3.1",
     "sass": "^1.14.1",
-    "serve-favicon": "^2.5.0"
+    "serve-favicon": "^2.5.0",
+    "styled-components": "^4.0.2"
   }
 }