enh(build) slimmer Docker image and add .dockerignore (#2719)

* use node:12-slim base image + minor cleanups
* do not copy unnecessary things into the Docker images

- The use of `node:12-slim` as a base image dramatically decreases Docker image size (from 1.1 GB to 342 MB).

Author: kaczmarj

.dockerignore

@@ -0,0 +1,15 @@
+.DS_Store
+build
+docs/_build
+__pycache__
+*.swp
+node_modules
+.project
+
+# editors
+.idea/
+.vscode/
+.Rproj.user
+
+# misc
+/work

Dockerfile

@@ -1,10 +1,22 @@
-FROM node:12
-# docker build -t highlight-js .
-RUN apt-get update && apt-get install -y nginx
+# Dockerfile for highlight.js
+#
+# Build image:
+#   docker build -t highlight-js .
+#
+# Run container:
+#   docker run --rm -it --publish 8080:80 highlight-js
+#
+#   And open a browser to http://localhost:8080
+
+FROM node:12-slim
+RUN apt-get update -qq \
+    && apt-get install --yes --no-install-recommends \
+        nginx \
+    && rm -rf /var/lib/apt/lists/*
 WORKDIR /var/www/html
-COPY ./package*.json /var/www/html/
+COPY package*.json /var/www/html/
 RUN npm install
-COPY . /var/www/html
+COPY . .
 RUN node tools/build.js :common
 EXPOSE 80
 CMD ["nginx", "-g", "daemon off;"]