Add ticket reference

Author: Sean Sullivan

elastic_datashader/tilegen.py

@@ -1271,8 +1271,9 @@ def remap_bucket(bucket, search):
                 categories.insert(0, categories.pop(categories.index("Other")))
             except ValueError:
                 pass
-            
+
             # datashader has issue in 0.15.0 with categories that have only one class
+            # https://github.com/holoviz/datashader/issues/1230
             if len(categories) == 1:
                 categories.append('')
             cat_dtype = pd.api.types.CategoricalDtype(categories=categories, ordered=True)