Use yarn.lock when building docker containers (#1348)

Author: matrus2

Dockerfile

@@ -4,6 +4,7 @@ FROM node:7.9.0-alpine
 WORKDIR /usr/src/app
 
 COPY ./build/package.json .
+COPY ./build/yarn.lock .
 
 # Install Node.js dependencies
 RUN yarn install --production --no-progress

tools/copy.js

@@ -29,6 +29,7 @@ async function copy() {
       },
     }, null, 2)),
     copyFile('LICENSE.txt', 'build/LICENSE.txt'),
+    copyFile('yarn.lock', 'build/yarn.lock'),
     copyDir('public', 'build/public'),
   ]);