security: update security@ PGP key

The key was renewed, but the gist linked in the repo wasn't updated.

README.md

@@ -94,7 +94,7 @@ any issues regarding security or privacy, please disclose the information
 responsibly by sending an email to security at lightning dot engineering,
 preferably encrypted using our designated PGP key
 (`91FE464CD75101DA6B6BAB60555C6465E5BCB3AF`) which can be found
-[here](https://gist.githubusercontent.com/Roasbeef/6fb5b52886183239e4aa558f83d085d3/raw/5fa96010af201628bcfa61e9309d9b13d23d220f/security@lightning.engineering).
+[here](https://gist.githubusercontent.com/Roasbeef/6fb5b52886183239e4aa558f83d085d3/raw/1ecb328bbcf36f76ead67f08008f8db1da07e60e/security@lightning.engineering).
 
 ## Further reading
 * [Step-by-step send payment guide with docker](https://github.com/lightningnetwork/lnd/tree/master/docker)

SECURITY.md

@@ -8,4 +8,4 @@ The last major lnd release is to be considered the current support version. Give
 
 To report security issues, send an email to security@lightning.engineering (this list isn't to be used for support). 
 
-The following key can be used to communicate sensitive information: `91FE 464C D751 01DA 6B6B  AB60 555C 6465 E5BC B3AF`. 
+The following key can be used to communicate sensitive information: [`91FE 464C D751 01DA 6B6B  AB60 555C 6465 E5BC B3AF`](https://gist.githubusercontent.com/Roasbeef/6fb5b52886183239e4aa558f83d085d3/raw/1ecb328bbcf36f76ead67f08008f8db1da07e60e/security@lightning.engineering).