Speed up deployments with image pre-pulling

Overview

In this release we pre-pull images before removing an existing function during its update. It will reduce the downtime between deletion and recreation by the image pull time.

Changelog for 0.9.11:

• PR #145 Pre-pull images during function updates by @alexellis
• PR #131 add Caddy to the install script by @jsiebens
• PR #139 Update faas-provider to v0.15.3 by @utsavanand2

Commits
9c04b8d Reduce duplication of pre-pull logic by @alexellis
c493613 Pre-pull images for updates by @alexellis
87f9938 Add known issue by @alexellis
9cdcac2 make email address optional by @jsiebens
a8a3d73 add Caddy to the install script by @jsiebens
f339643 Add use-cases by @alexellis
03ad56e Highlight the bash installer as an option by @alexellis
baea300 Update faas-provider to v0.15.3 by @utsavanand2
cb786d7 Bump minor version of faasd to 0.9.10 by @alexellis
fc02b4c Update vendor for openfaas components by @alexellis
ecee5d6 Fix publish Makefile target by @alexellis

Generated by Derek