Correct wikipedia link re: sparse index

Author: epc

source/core/indexes.txt

@@ -492,7 +492,7 @@ By default, ``sparse`` is ``false`` on MongoDB indexes.
    reject documents that have duplicate values for a field, but that
    ignore documents that do not have the key.
 
-   .. _`block-level`: http://en.wikipedia.org/wiki/Index_%28database%29#Sparse_index>
+   .. _`block-level`: http://en.wikipedia.org/wiki/Database_index#Sparse_index
 
 .. [#null-values-are-indexed-in-sparse-indexes] All documents that
    have the indexed field *are* indexed in a sparse index, even if