cbuildbot_config_unittest: Fix path to config_dump.json in assertion message

BUG=none
TEST=none

Change-Id: I47cc2200913ce77882f727ac705f89c1a192f7b2
Reviewed-on: https://chromium-review.googlesource.com/203105
Commit-Queue: Gaurav Shah <gauravsh@chromium.org>
Tested-by: Gaurav Shah <gauravsh@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
1 file changed