Revert "Update instructor-notes.md"

This reverts commit f8709cf.

Undoing test commits I made as I was trying to trigger a site rebuild.
I figured out how to do that, so had to remove 2 bits of 'test'
text that I had added.

Author: jonjab

instructors/instructor-notes.md

@@ -80,7 +80,15 @@ from this data.
 
 ## Error message
 
+> ```
+> Error in grid.Call(C_textBounds, as.graphicsAnnot(x$label), x$x, x$y,  : 
+> ```
 
+polygon edge not found
+
+> ```
+> {: .error}
+> ```
 
 #### [Explore and Plot by Shapefile Attributes](07-vector-shapefile-attributes-in-r.md)