fix wiki link to SQL mapping

Author: epc

source/index.txt

@@ -139,7 +139,7 @@ MongoDB. The following pages from the wiki are especially useful:
         - :wiki:`Introduction`
         - :wiki:`Downloads`
         - :wiki:`Features`
-        - :wiki:`SQL to MongoDB Mapping <SQL+to+MongoDB+Mapping+Chart>`
+        - :wiki:`SQL to MongoDB Mapping <SQL+to+Mongo+Mapping+Chart>`
 
    - :wiki:`Developer Documentation <Developer+Zone>`