Update console.go

[phonikg]

Lower resource devices(e.g.- Raspberry Pi B+) with low CPU freq and 512MB of ram or less cannot complete processes within the current 5 second time limit. Suggesting 40 seconds, although this is not perfect as error still occurs, but at least command seems to be processed in the end, with a delay.

e.g.:

personal.newAccount()
Passphrase:
Repeat passphrase:
Invalid JSON RPC response: {"error":{"code":-32603,"context deadline exceeded":"context deadline exceeded"},"id":4,"version":"2.0"}

[phonikg]

This shed some light on it for me, see karalbe's comments at bottom of issue:

ethereum#2901