change outdated seed to keystore

[garrettian]

No description provided.

[lsaether]

I believe the --keystore-path flag is not a drop-in replacement for the old --key flag. Instead keys are managed by the node and require RPC methods either author_setKey or author_rotateKeys. The --keystore-path flag has always existed even alongside the --key flag and determines which directory to keep keys in the node.