Use PUT verb for function updates.
Use PUT verb for function updates.

As discussed in openfaas/faas#208, this commit switches the verb used
for updates from the non-HTTP UPDATE to PUT.

Signed-off-by: John McCabe <a51dda7c7ff50b61eaea0444371f4a6a9301e501@johnmccabe.net>

itscaro/faas-cli,itscaro/faas-cli,itscaro/faas-cli