Update SecurityConcerns.md

module4/labs/Week3/SecurityConcerns.md

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 title: Security Concerns Lab
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-<section class='call-to-action' markdown='1'>
+<section class='instructor-notes' markdown='1'>
 
 Encourage students to reach out to each other during this lesson.  If they complete it, they will be almost there on implementing authorization; we don't need them to get through the whole thing, but it would be good to wrap up with a short discussion of how we would compare two digests (database value to user input).