fix grammar in calendar events api "important_dates" parameter
fix grammar in calendar events api "important_dates" parameter

since the newline isn't significant in the rendered docs, the
existing code read as "Defaults to false if true, ..."

put a period in there to clarify "Defaults to false. If true, ..."

test plan: render docs

flag = none

closes LS-2843

Change-Id: Ifc0917b1a5da20e1f49217a0eaee836ba043cb69
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/278283
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Eric Saupe <e7287cf05ae62bc45889f17a9d34b8fae8d5afd1@instructure.com>
QA-Review: Eric Saupe <e7287cf05ae62bc45889f17a9d34b8fae8d5afd1@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

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