DOC: Update whatsnew

Author: addisonlynch

docs/source/whatsnew/v0.8.0.txt

@@ -31,6 +31,7 @@ Enhancements
 - Added testing on Python 3.7 (:issue:`667`)
 - Allow IEX to read less than 1 year of data (:issue:`649`)
 - Allow data download from Poland using stooq (:issue:`597`)
+- All time series readers now use a rolling default starting date (most are 15 years before the current date. Intraday readers are 3-5 days from the current date)
 
 .. _whatsnew_080.api_breaking:
 
@@ -63,6 +64,7 @@ Bug Fixes
 - Adjust Alphavantage time series reader to account for descending ordering. (:issue:`666`)
 - Fix bug in downloading index historical constituents. (:issue:`591`)
 - Fix a bug that occurs when an endpoint returns has no data for a date range. (:issue:`640`)
+- Fix a bug that caused an exception to be raised when IEX default dates are used (:issue:`607`)
 
 Contributors
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