doc: update SECURITY.md inline with recent changes to bitcoincore.org

See bitcoin-core/bitcoincore.org#809 and
bitcoin-core/bitcoincore.org#819 and
https://bitcoincore.org/en/contact/.

Author: fanquake

SECURITY.md

@@ -14,7 +14,7 @@ The following keys may be used to communicate sensitive information to developer
 | Name | Fingerprint |
 |------|-------------|
 | Wladimir van der Laan | 71A3 B167 3540 5025 D447  E8F2 7481 0B01 2346 C9A6 |
-| Jonas Schnelli | 32EE 5C4C 3FA1 5CCA DB46  ABE5 29D4 BCB6 416F 53EC |
 | Pieter Wuille | 133E AC17 9436 F14A 5CF1  B794 860F EB80 4E66 9320 |
+| Michael Ford | E777 299F C265 DD04 7930  70EB 944D 35F9 AC3D B76A |
 
 You can import a key by running the following command with that individual’s fingerprint: `gpg --recv-keys "<fingerprint>"` Ensure that you put quotes around fingerprints containing spaces.