Nightly builds don't include bundles

Environment

See https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/jobs/95693359

Steps to reproduce

Run "build" step in pipeline on release-2018-5 branch.

Observed behavior

Console output contains the line

npm WARN lifecycle adblockplusui@~postinstall: cannot run in wd %s %s (wd=%s) adblockplusui@ npm run bundle /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockplusui

followed by one such line for each bundle it is supposed to create

Warning: Mapped file adblockplusui/first-run.js doesn't exist

Expected behavior

No such warnings are included in the console output.

Further information

Relevant console output:

$ python build.py build -t gecko -b ${CI_COMMIT_SHA:0:8} adblockplus.xpi
INFO: Cloning repository https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@gitlab.com/eyeo/adblockplus/abpui/adblockpluscore into /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockpluscore
INFO: Updating repository /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockpluscore to revision 16febf9027a34d7a9fc680e375dce988cf43f7cd
INFO: Cloning repository https://github.com/adblockplus/buildtools into /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockpluscore/buildtools
INFO: Updating repository /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockpluscore/buildtools to revision 93e54d41ef7b2d1441f81b01822cbabac11fb84c
INFO: Cloning repository https://github.com/adblockplus/jshydra into /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockpluscore/buildtools/jshydra
INFO: Updating repository /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockpluscore/buildtools/jshydra to revision 104e6202a38ab8e9ecec6a5faa91e2124212d8d1
INFO: Cloning repository https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@gitlab.com/eyeo/adblockplus/abpui/adblockplusui into /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockplusui
INFO: Updating repository /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockplusui to revision 51608208fcb7c2b5c251eb64b5c52185ed5d660e
npm WARN lifecycle adblockplusui@~postinstall: cannot run in wd %s %s (wd=%s) adblockplusui@ npm run bundle /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockplusui
INFO: Cloning repository https://github.com/adblockplus/buildtools into /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockplusui/buildtools
INFO: Updating repository /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/adblockplusui/buildtools to revision 3c6d11821dcb1e2aaf0292f0ff604c076b99dd36
INFO: Cloning repository https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@gitlab.com/eyeo/adblockplus/abpui/buildtools into /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/buildtools
INFO: Updating repository /builds/eyeo/adblockplus/abpui/adblockplusui/adblockpluschrome/buildtools to revision deb79b07b48f311395d7cda194df142ea322d3ba
Warning: Mapped file adblockplusui/first-run.js doesn't exist
Warning: Mapped file adblockplusui/skin/first-run.css doesn't exist
Warning: Mapped file adblockplusui/issue-reporter.js doesn't exist
Warning: Mapped file adblockplusui/skin/issue-reporter.css doesn't exist
Warning: Mapped file adblockplusui/desktop-options.js doesn't exist
Warning: Mapped file adblockplusui/skin/desktop-options.css doesn't exist
Warning: Mapped file adblockplusui/popup.js doesn't exist
Warning: Mapped file adblockplusui/skin/popup.css doesn't exist
Warning: Mapped file adblockplusui/skin/web.css doesn't exist
Warning: locale string add defined multiple times