Using latest version every time is just asking for weird random issues.
This commit in `gomobile` has made Go `1.16` required:
80cb72e7af
Since we upgarded Go to 1.16 on CI hosts we can now use the recommended
method of installing tools, which is using `go install`.
In addition to that I've pinned other tools that we install to specific
versions, and dropped use of `modvendor` fork thanks to merging of:
https://github.com/goware/modvendor/pull/13
Signed-off-by: Jakub Sokołowski <jakub@status.im>