Fixed #8581: Corrected example of "grep" to search docs

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8736 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/intro/whatsnext.txt

@@ -159,7 +159,7 @@ Django document:
 
 .. code-block:: bash
 
-    $ grep -r max_length /path/to/django/docs/*.txt
+    $ grep -r max_length /path/to/django/docs/
     
 As HTML, locally
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