As a workaround I used nvm to install an appropriate version for npm:
export NODE_VERSION=0.12.8 && \ curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.1/install.sh | bash && \ export NVM_DIR="/root/.nvm" && \ source $NVM_DIR/nvm.sh && \ nvm install v$NODE_VERSION && \ ln -s /root/.nvm/versions/node/v0.12.8/bin/npm /usr/bin/npm