fix typo in docker setup readme
fix typo in docker setup readme

Change-Id: I61a6e1ca8632ca5839875125eb407f2a99835999
Reviewed-on: https://gerrit.instructure.com/133909
Tested-by: Jenkins
Reviewed-by: Michael Brewer-Davis <785693f4c81267e5b88c0f98d39b56a39a2b6910@instructure.com>
Product-Review: Neil Gupta <cc4fec8a34766005dd45d48be045c08d736c11ed@instructure.com>
QA-Review: Neil Gupta <cc4fec8a34766005dd45d48be045c08d736c11ed@instructure.com>

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