Revert "docgen: --cache off for tests"

This reverts commit 0a8a7a57e7a6b4b5a0d1523bde57b2a4b93fa50a.

This workaround is no longer necessary.
3ff0e8bd96Andrew Kelley committed on 3/11/2019, 2:35:42 PMparent6a5c2b2
1 file changedLine totals unavailable