Fix wrong number of presenters

Author: koendehondt

Chapters/MailApp/MailApp.md

@@ -276,7 +276,7 @@ That concludes our models. Now we can dig into the presenters.
 
 ### The presenters
 
-Many presenters are composed of smaller presenters. That is also the case here. We need a presenter to display an email. We also need a presenter to display the tree of emails. When no email is selected in the tree, we like to display an informational message. That is also a presenter. And the overall application, that ties everything together, is also a presenter. So we have four presenters:
+Many presenters are composed of smaller presenters. That is also the case here. We need a presenter to display an email. We also need a presenter to display the tree of emails. When no email is selected in the tree, we like to display an informational message. That is also a presenter. And the overall application, that ties everything together, is also a presenter. So we have five presenters:
 
 * `EmailPresenter` displays an `Email`, either editable or read-only. The fields are editable when the email is draft. The fields are read-only when the email is received or sent.
 * `NoEmailPresenter` displays an informative message to tell that no email has been selected.