Update version used to build faktory for docker

[jssblck]

I encountered an error when running Faktory using the official contribsys/faktory image hosted on Ubuntu 20.04:

runtime: mlock of signal stack failed: 12
runtime: increase the mlock limit (ulimit -l) or
runtime: update your kernel to 5.3.15+, 5.4.2+, or 5.5+
fatal error: mlock failed

This error is traced to this Go issue, in which Go works around a Linux kernel bug. The ultimate resolution of that issue is that once a docker host is upgraded to Ubuntu 20.04, the Go workaround breaks Faktory. This workaround was special cased for Ubuntu in go1.14.1 (Ubuntu cherry picked the kernel fix into a seemingly older kernel, which Go then tries to apply the work around, then dies).

This PR bumps the CircleCI build image for Faktory to use go1.14.9, which was chosen so contribsys/faktory would still be on go1.14.x (if you want to bump it further, of course feel free).

[mperham]

Doesn’t “1.14” pick the latest patch release?

[mperham]

Faktory 1.4.2 coming RSN will use Go 1.15.