[title] Fix issue with non-string names in series title (apache#5433)

(cherry picked from commit 4e3b2e7)

superset/viz.py

@@ -1389,11 +1389,9 @@ def get_data(self, df):
                 continue
             if isinstance(name, string_types):
                 series_title = name
-            elif len(self.metrics) > 1:
-                series_title = ', '.join(name)
             else:
-                l = [str(s) for s in name[1:]]  # noqa: E741
-                series_title = ', '.join(l)
+                offset = 0 if len(metrics) > 1 else 1
+                series_title = ', '.join([text_type(s) for s in name[offset:]])
             values = []
             for i, v in ys.iteritems():
                 x = i