change dockerfile to use mozilla/ci-docker-bases

Dockerfile

@@ -1,18 +1,10 @@
 
-FROM python:3.7.4
+FROM mozilla/cidockerbases:therapist-latest
 
 WORKDIR /app
 
-RUN curl -sL https://deb.nodesource.com/setup_10.x | bash -
-RUN apt-get install -y nodejs
-
-RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
-RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
-RUN apt-get update && apt-get install yarn
-
 COPY ./package.json /app/package.json
 COPY ./yarn.lock /app/yarn.lock
 RUN yarn install
 
-
-COPY . /app
+COPY . /app