Tiny fixes in docstrings for the geom_count() and stat_sum().

Author: ASmirnov-HORIS

python-package/lets_plot/plot/geom.py

@@ -6455,7 +6455,7 @@ def geom_count(mapping=None, *, data=None, stat=None, position=None, show_legend
                color_by=None, fill_by=None,
                **other_args):
     """
-    Sum unique values
+    Sum unique values.
 
     Parameters
     ----------

python-package/lets_plot/plot/stat.py

@@ -459,7 +459,7 @@ def stat_sum(mapping=None, *, data=None, geom=None, position=None, show_legend=N
              color_by=None, fill_by=None,
              **other_args):
     """
-    Sum unique values
+    Sum unique values.
 
     Parameters
     ----------