try to address pandas installation failure

Author: emmanuelle

Diff for: packages/python/plotly/tox.ini

@@ -59,7 +59,7 @@ deps=
     pytz==2016.10
     retrying==1.3.3
     pytest==3.5.1
-    pandas==0.19.2
+    pandas==0.25.1
     backports.tempfile==1.0
     optional: --editable=file:///{toxinidir}/../plotly-geo
     optional: numpy==1.11.3