Added note to whatsnew doc

Author: josephtole

docs/source/whatsnew/v0.9.0.txt

@@ -29,6 +29,7 @@ Bug Fixes
 ~~~~~~~~~
 
 - Fix Yahoo! actions bug due to change in split format. (:issue: `755`)
+- Fix FutureWarning from pandas import. (:issue: `762`)
 
 Contributors
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