Add missing value for Image in /system/function/NAME response

Changelog for 0.15.0-rc3:

• PR #246 Add missing value for Image in /system/function/NAME response by @welteki
• PR #237 Updated install.sh to include iptables by @rvramesh
• PR #242 Bump github.com/docker/distribution from 2.7.1+incompatible to 2.8.0+incompatible by @dependabot[bot]

Commits
4b13231 Fix #245 missing image value by @welteki
ab47082 Removed iptables dependency for Red Hat / CentOS and Arch Linux by @rvramesh
b807ff0 Updated install.sh to include iptables by @rvramesh
f74f5e6 Bump github.com/docker/distribution by @dependabot[bot]
95c41ea Update faas-provider and gateway by @alexellis

Changes: 0.15.0-rc2...0.15.0-rc3

Generated by Derek