Error when building from source with source maps.

[SylvainCorlay]

When building from source, the last stage of jlpm run build yields

Failed to parse source map from '/home/sylvain/dev/jupyterlite/xeus-python-kernel/node_modules/@jupyterlite/server/src/app.ts' file: Error: ENOENT: no such file or directory, open '/home/sylvain/dev/jupyterlite/xeus-python-kernel/node_modules/@jupyterlite/server/src/app.ts'

It seems that the source map files are in server/lib instead of server/src.