Upgrade python, node, yarn.

Dockerfile

@@ -1,5 +1,5 @@
 # ================ PYTHON
-FROM python:3.8.1
+FROM python:3.8.2
 
 # System setup:
 RUN apt-get update \
@@ -16,7 +16,8 @@ RUN pip install pip-tools
 RUN groupadd --gid 1000 node \
   && useradd --uid 1000 --gid node --shell /bin/bash --create-home node
 
-ENV NODE_VERSION 12.14.1
+ENV NODE_VERSION 12.16.1
+
 RUN ARCH= && dpkgArch="$(dpkg --print-architecture)" \
   && case "${dpkgArch##*-}" in \
     amd64) ARCH='x64';; \
@@ -52,9 +53,13 @@ RUN ARCH= && dpkgArch="$(dpkg --print-architecture)" \
   && grep " node-v$NODE_VERSION-linux-$ARCH.tar.xz\$" SHASUMS256.txt | sha256sum -c - \
   && tar -xJf "node-v$NODE_VERSION-linux-$ARCH.tar.xz" -C /usr/local --strip-components=1 --no-same-owner \
   && rm "node-v$NODE_VERSION-linux-$ARCH.tar.xz" SHASUMS256.txt.asc SHASUMS256.txt \
-  && ln -s /usr/local/bin/node /usr/local/bin/nodejs
+  && ln -s /usr/local/bin/node /usr/local/bin/nodejs \
+  # smoke tests
+  && node --version \
+  && npm --version
+
+ENV YARN_VERSION 1.22.4
 
-ENV YARN_VERSION 1.21.1
 RUN set -ex \
   && for key in \
     6A010C5166006599AA17F08146C2130DFD2497F5 \
@@ -70,7 +75,9 @@ RUN set -ex \
   && tar -xzf yarn-v$YARN_VERSION.tar.gz -C /opt/ \
   && ln -s /opt/yarn-v$YARN_VERSION/bin/yarn /usr/local/bin/yarn \
   && ln -s /opt/yarn-v$YARN_VERSION/bin/yarnpkg /usr/local/bin/yarnpkg \
-  && rm yarn-v$YARN_VERSION.tar.gz.asc yarn-v$YARN_VERSION.tar.gz
+  && rm yarn-v$YARN_VERSION.tar.gz.asc yarn-v$YARN_VERSION.tar.gz \
+  # smoke test
+  && yarn --version
 
 # ================ ENVIRONMENT
 ENV PYTHONUNBUFFERED 1