build: don't build twice on deploy

On deploy the build step is executed twice. As configured in
`travis.yml` and in the `prepublish` hook in `package.json`.

Author: gruhn

package.json

@@ -23,7 +23,6 @@
     "build": "npm run build:browser && npm run build:common",
     "build:browser": "cross-env NODE_ENV=production webpack --config config/webpack.config.browser.js --progress --hide-modules",
     "build:common": "cross-env NODE_ENV=production webpack --config config/webpack.config.common.js --progress --hide-modules",
-    "prepublish": "npm run build",
     "unit": "cross-env BABEL_ENV=test karma start test/unit/karma.conf.js --single-run",
     "e2e": "node test/e2e/runner.js",
     "test": "npm run unit && npm run e2e",