Bumped version of node to 7.0.0

Dockerfile

@@ -1,4 +1,4 @@
-FROM node
+FROM node:7
 
 # Create app directory
 RUN mkdir -p /usr/src/app

circle.yml

@@ -1,6 +1,6 @@
 machine:
   node:
-    version: 6
+    version: 7
   services:
     - docker
 

package.json

@@ -84,5 +84,8 @@
     "webpack-hot-middleware": "^2.12.2",
     "webpack-module-hot-accept": "^1.0.4",
     "whatwg-fetch": "^1.0.0"
+  },
+  "engines": {
+    "node": ">=7.0.0"
   }
 }