another typo

Author: jmalkin

docs/source/helper/index.rst

@@ -8,7 +8,7 @@ functionality within sketches.
 Some of them are abstract base classes, but in those cases there is at
 least one reference example of a concrete class.
 
-  * :class:`serde` is used when serializing and deserializing sketches/
+  * :class:`serde` is used when serializing and deserializing sketches.
   * :class:`jaccard` is used to compute the Jaccard similarity between pairs of theta or tuple sketches.
   * :class:`tuple_policy` is required to use a :class:`tuple_sketch` by specifying how summaries are combined.
   * :func:`ks_test` performs a Kolmogorov-Smirnov test on absolute-error quantiles family sketches.