Install npm 3.3.12 manually in CircleCI

Now CircleCI doesn't contain npm 3.x
https://discuss.circleci.com/t/wrong-npm-version-with-node-5-0-5-1/827

circle.yml

@@ -13,6 +13,8 @@ dependencies:
   cache_directories:
     - "~/.electron"
     - "src/node_modules"
+  pre:
+    - npm install -g npm@3.3.12
   post:
     - mkdir -p ~/.electron
     - docker run --rm -it -v `pwd`:/home/xclient/electron-mattermost -v ~/.electron:/home/xclient/.electron yuyaoc/em-builder:dev ./electron-mattermost/docker/package_in_docker.sh