Fix docker build (#2348)

* .eslintrc.json is required to build using react-scripts

* Remove the extra "deps" step

This step can be done as part of the build (faster and more reliable).

* Add a GitHub Actions to build the Docker image

Make sure that "docker build" is working on every pull request before landing on master.

* Update package-lock.json

* Add .prettierrc in the Docker image to avoid warnings in the build step

* Revert "Update package-lock.json"

This reverts commit 7ef2eaadfa.

* Make sure that the 'node_modules' layer can be cached

if package and package-lock.json didn't changed

.github/workflows/build-docker.yml

@@ -0,0 +1,15 @@
+name: Build Docker image
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  build-docker:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - run: docker build -t excalidraw .