Update source/runbooks/manage-an-incident.html.md.erb

Co-authored-by: ewastempel <52969218+ewastempel@users.noreply.github.com>

source/runbooks/manage-an-incident.html.md.erb

@@ -29,7 +29,7 @@ For ease of use the key steps are documented within the overview, with further d
  create a pager-duty incident (ensuring it is on the external status page) and a slack channel
 ###3.	Assign roles.
 Incident Lead and Scribe are mandatory roles
-###4.	Managing the incident
+###4. Managing the incident
 including communication - and who to tell
 ###5. Fixing the problem
 ###6. Post-incident procedure