chore: update clade_emergence_dates for 21I (Delta) and 21J (Delta)
Dates were copied from 21A (Delta)
@@ -19,5 +19,6 @@ Nextstrain_clade first_sequence
21E (Theta) 2021-01-10
21F (Iota) 2020-11-20
21G (Lambda) 2021-01-05
-21H 2021-01-05
21H (Mu) 2021-01-05
+21I (Delta) 2020-10-30
+21J (Delta) 2020-10-30
