Update npm version to 2.15.3 in package.json and circle

circle.yml

@@ -18,6 +18,7 @@ dependencies:
     - sudo service mongod restart
     - lein deps
     - pip install awscli==1.7.3
+    - npm install -g npm@2.15.3
 database:
   post:
     # MySQL doesn't load named timezone information automatically, you have to run this command to load it

package.json

@@ -7,7 +7,7 @@
   "license": "private",
   "engines": {
     "node": "4.4.3",
-    "npm": "2.15.1"
+    "npm": "2.15.3"
   },
   "dependencies": {
     "ace-builds": "^1.2.2",