upgrade npm in dev container

Author: blakeblackshear

docker/Dockerfile.dev

@@ -22,3 +22,5 @@ RUN pip3 install pylint black
 # Install Node 14
 RUN curl -sL https://deb.nodesource.com/setup_14.x | bash - \
     && apt-get install -y nodejs
+
+RUN npm install -g npm@latest