Add release date of 3.5.8 final (#1591)

https://github.com/python/cpython/releases/tag/v3.5.8

Author: hugovk

pep-0478.txt

@@ -69,6 +69,7 @@ including their release dates.
 - 3.5.7 final: March 18, 2019
 - 3.5.8 candidate 1: September 9, 2019
 - 3.5.8 candidate 2: October 12, 2019
+- 3.5.8 final: October 29, 2019
 - 3.5.9 final: November 1, 2019
 - 3.5.10 rc1: August 21, 2020
 - 3.5.10 final: September 5, 2020