Added js linter config.

linting/js/Dockerfile

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+FROM node:12-alpine
+
+RUN mkdir /src
+
+# Hack to upgrade NPM:
+#  - install local version
+#  - replace old global verson with new one
+
+RUN npm install npm@5.3 && \
+    rm -rf /usr/local/lib/node_modules/npm && \
+    mv /node_modules/npm  /usr/local/lib/node_modules
+
+RUN npm install -g xo@0.24.0
+
+# Cleanup
+RUN rm -fr /root/.npm /node_modules
+
+WORKDIR /src
+
+ENTRYPOINT ["/usr/local/bin/xo"]

linting/js/eslintrc.yml

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+rules:
+    quotes:
+        - error
+        - double
+    unicorn/prefer-query-selector: off
+    no-negated-condition: off