fit search button and its content in grade history form
fit search button and its content in grade history form

fixes GRADE-329

test plan:
 1. Visit Gradebook History
 2. Resize the browser to a variety of arbitrary widths
 3. Verify that the search button is always visible
 4. Verify that the search button label is fully visible

Change-Id: I1daff3b47c21c9a01bf8946263ce644f33c5536d
Reviewed-on: https://gerrit.instructure.com/135558
Reviewed-by: Keith T. Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>
Reviewed-by: Spencer Olson <7cc0890d6f1f70810a023e7173eca5724d6c8e49@instructure.com>
Tested-by: Jenkins
Product-Review: Keith T. Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>
QA-Review: Keith T. Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>

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