This is failing on hub.docker.com (master / 3.6.1 release), and also on ci.moodle.org (integration / next), and also locally.
The job on ci.moodle.org has been failing since the 23rd March, and it's not possible to build locally on either branch using nvm at the latest LTS version.

This appears to match the release of cordova 9.0.0.

The Dockerfile is based on the documentation for the Moodle Mobile app (https://docs.moodle.org/dev/Setting_up_your_development_environment_for_Moodle_Mobile_2#Updating_ionic_and_cordova) which states to install cordova with:
npm install -g cordova

At the time that the Dockerfile was written, the supported version of Cordova was 8.1.2, which worked. However, since then cordova have pushed out version 9.0.0 (22nd March 2019), which breaks a number of plugins.

This issue will affect anyone using the instructions to run Moodle Mobile, regardless of Docker. The fact that we now have Docker images which are failing to build just means that we are aware of it now, rather than when someone at HQ does an `npm -g install cordova`.