Generate Diviner book for Javelin
Summary: And also fix a bug in the generator script.
Test Plan: Run bin/diviner generate, wait till the cows come home, see 3 pages about Javelin in the Diviner app.
Reviewers: O1 Blessed Committers, chris
Reviewed By: O1 Blessed Committers, chris
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25429