Update pandas for Python 3

Author: jonmmease

packages/python/plotly/tox.ini

@@ -57,7 +57,8 @@ deps=
     pytz==2016.10
     retrying==1.3.3
     pytest==3.5.1
-    pandas==0.24.2
+    pandas==0.24.2;python_version<"3.0"
+    pandas==1.2.0;python_version>"3.5"
     xarray==0.10.9
     statsmodels==0.10.2
     pillow==5.2.0