fix(build): add missing build step before releasing

Runs `yarn build` before releasing the bundle to npm. This was
step was forgotten when migrating the build to Github Actions.

fixes #173

Author: jamesfer

.github/workflows/default.yml

@@ -49,6 +49,7 @@ jobs:
         with:
           node-version: 12
       - run: yarn install --frozen-lockfile
+      - run: yarn build
       - run: yarn semantic-release
         env:
           GITHUB_TOKEN: ${{ secrets.github_token }}