Update to fix pandas 1.0.0 issue

Author: Kevin D Smith

swat/dataframe.py

@@ -415,9 +415,7 @@ def __init__(self, data=None, index=None, columns=None, dtype=None, copy=False,
         self.label = a2u(label)
         self.title = a2u(title)
         # TODO: Should attrs be walked and converted to unicode?
-        self.attrs = attrs
-        if self.attrs is None:
-            self.attrs = {}
+        self.attrs = attrs or {}
         self.formatter = formatter
         if self.formatter is None:
             self.formatter = SASFormatter()