23:30:33 npm ERR! EEXIST, symlink '../esprima/bin/esparse.js'
23:30:33 File exists: ../esprima/bin/esparse.js
23:30:33 Move it away, and try again.
Caused by a bug in npm or a bug in the dev-dependencies in how they register themselves with npm.
This error happens when two builds run in parallel on the same ci slave host.
A recheck usually "fixes" it for now.