fix migration version number generation
fix migration version number generation

ignore the brand config versions that aren't dates

Change-Id: Iecc774799e3ed7769a9590766e46f77d23ef2f41
Reviewed-on: https://gerrit.instructure.com/129055
Tested-by: Jenkins
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms