Pin the version of staticcheck that we use
Each version of staticcheck contains different rules, and over time the same rule may change.
Since we currently fetch master
of the staticcheck tool, our build can break when a change arrives in the staticcheck tool.
We should pin the version of staticcheck that we use and update is consciously when we chose to, if we want to avoid random broken builds.
This is a first attempt at this.
Related slack thread: https://gitlab.slack.com/archives/C2TDMHW69/p1564555848004200