[server/sources] fix name error in eid_type_source_pre_131
i.e. the eid_type_source implementation used when some pre 3.13.1
database is detected. Regression from 5fbdbbe51867.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html