Change [ERR] message to [ERROR]

[aphorise]

Is it possible to do a small change on the error in protocol.go:

log.Printf("[ERR] Failed to read proxy prefix: %v", err)
to
log.Printf("[ERROR] Failed to read proxy prefix: %v", err)

At present there are portion of Vault logs where this does not align:

… vault1 vault[11406]: … [ERROR] core: unlocking HA lock failed: error="cannot find peer"
… vault1 vault[11406]: … [ERROR] storage.raft.raft-net: failed to accept connection: error="Raft RPC layer closed"
… vault1 vault[11406]: … [ERR] Failed to read proxy prefix: read tcp4 …:8200->…:36236: read: connection reset by peer 

I can do a PR around this but I'm not sure if it could potentially impact other forks / builds using this else where?

[aphorise]

Closing request - as I've had a change of heart upon further review of other dependencies used in Vault and since requesting the above.

It seems that there's an informal pattern in many other packages used in Vault which also report with [ERR] type entries that are actually rather useful to discern from other [ERROR] type entries where the former ([ERR]) can only be from dependencies.