CI broken - "npm not found"

See https://gitlab.idiap.ch/beat/beat.editor/-/jobs/152718, specifically the line:

/local/builds/beat/beat.editor/miniconda/conda-bld/beat.editor_1543860509476/work/conda_build.sh: line 5: npm: command not found

This is in the build step, so it doesn't concern the testing docker image.