increase calendar view navigation arrows to 12px from 10px
increase calendar view navigation arrows to 12px from 10px

Refs: CNVS-26581

test plan:
- as a user using the old and/or new ui
- navigate to the calendar view
- inspect the navigation arrows above the month view
- this is where to looK: http://screencast.com/t/5xlxVgpV2IF

Change-Id: I2719a1beebfb2611d8037257bfde1f3a61014858
Reviewed-on: https://gerrit.instructure.com/72796
Tested-by: Jenkins
Reviewed-by: Chris Hart <b82b40b84a2f06957ec9caf1768340bd6b929cc4@instructure.com>
Product-Review: Chris Hart <b82b40b84a2f06957ec9caf1768340bd6b929cc4@instructure.com>
QA-Review: Myller de Araujo <e5c7c5e1b7f2ce5e9870cc98ec52b20b3006cb48@instructure.com>

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