Multiple improvements of code quality

[paskal]

• bump go modules
• bump github.com/alicebob/miniredis to v2
• match linter settings with remark42 project, fix found issues
• replace assert.Nil(t, err) with NoError calls, as well as NotNil with Error
• start running cache examples, make them work offline
• introduce LoadingCache.Close function
• add proper teardown to tests to prevent goroutine leak

Please merge with rebase.