update for 0.20

[jlopp]

$ ./bitcoind-v0.19 --help --help-debug|grep "^ -" | sort > ./options-0.19.txt
$ ./bitcoind-v0.20 --help --help-debug|grep "^ -" | sort > ./options-0.20.txt
$ diff -du ./options-0.19.txt ./options-0.20.txt

--- ./options-0.19.txt 2020-05-26 17:17:09.237383284 -0400
+++ ./options-0.20.txt 2020-05-26 17:16:46.909338756 -0400
@@ -4,6 +4,7 @@

+  -asmap=<file>
-  -enablebip61
-  -logthreadnames
+  -rpcwhitelistdefault
+  -rpcwhitelist=<whitelist>