Fix typo: remove unnecessary quotes
`:edit "foo.txt"` -> `:edit foo.txt`
    
        | author | Richard Cheng <rcheng@neuratron.com> | 
    
        | date | Tue, 17 Apr 2012 10:24:45 +0100 | 
    
    
        | parents | 751620ce9fae | 
    
        | children | b00b5355c40f | 
    
        | branches/tags | (none) | 
    
        | files | chapters/28.markdown | 
Changes
    
--- a/chapters/28.markdown	Mon Apr 16 15:23:50 2012 +0100
+++ b/chapters/28.markdown	Tue Apr 17 10:24:45 2012 +0100
@@ -12,7 +12,7 @@
 build commands out of arbitrary strings.
 
 Let's try a more useful example.  Prepare by opening a file in Vim, then using
-`:edit "foo.txt"` in the same window to open a new buffer.  Now run the
+`:edit foo.txt` in the same window to open a new buffer.  Now run the
 following command:
 
     :::vim