converts rubrics/user_index js_block into js_bundle

test plan:
* regression test rubric editing

Change-Id: I71427adcdcc4c579a1f2dba0c074fdbea0e16ae8
Reviewed-on: https://gerrit.instructure.com/29116
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>