[simple-scan] help: Fix typo (apper -> appear)

[Piotr Drąg <piotrdrag src gnome org>]

commit c3f03279f324695b7749047d5606a1eff53bb594
Author: Anders Jonsson <anders jonsson norsjovallen se>
Date:   Mon Sep 18 14:21:09 2017 +0200

    help: Fix typo (apper -> appear)
    
    https://bugzilla.gnome.org/show_bug.cgi?id=787830

 help/C/crop.page |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/help/C/crop.page b/help/C/crop.page
index b65893e..ab0bf64 100644
--- a/help/C/crop.page
+++ b/help/C/crop.page
@@ -11,7 +11,7 @@
     <p>
     The cropping feature in <app>Simple Scan</app> allows you to use only a part of a scanned image. You can
     enable crop either before or after scanning a page, and you can always change the dimensions of the crop
-    frame. When crop is enabled, a mask will apper over the current page with the area not being used shown
+    frame. When crop is enabled, a mask will appear over the current page with the area not being used shown
     in gray. You can enable crop and choose the desired dimensions via one of the following methods:
     </p>