upgrade cli package, fix drone 1.x token env variable issue

[oliver-nyt]

This should fix #119 by picking up both the PLUGIN_TOKEN (drone 1.x) and TOKEN(drone 0.x) env variables (see main.go line 93)
I upgraded the cli package to v2 before I noticed that you can do this in v1 as well. I can undo that change if you prefer so.

[montmanu]

LGTM! Just a couple of "nice to haves" ..

• Update references to TOKEN in documentation
• Update references to TOKEN in Makefile
• Add unit tests for token param precedence? Something like:

func TestTokenParamPrecedence(t *testing.T) {
    // Reset environment
    os.Clearenv()

    // Set both token-related environment variables
    os.Setenv("TOKEN", "from-token-env")
    os.Setenv("PLUGIN_TOKEN", "from-plugin-token-env")

    // Set token CLI argument
    set := flag.NewFlagSet("prefer-arg-over-any-env", 0)
    c := cli.NewContext(nil, set, nil)
    set.String("token", "from-token-arg", "")
    
    // token CLI argument takes precedence over either environment variable
    assert.Equal(t, c.String("token"), "from-token-arg")

    // Reset environment
    os.Clearenv()

    // Set both token-related environment variables
    os.Setenv("TOKEN", "from-token-env")
    os.Setenv("PLUGIN_TOKEN", "from-plugin-token-env")

    // Set CLI arguments without token
    set = flag.NewFlagSet("prefer-plugin-token-env", 0)
    c = cli.NewContext(nil, set, nil)

    // PLUGIN_TOKEN environment variable takes precedence over TOKEN environment variable
    assert.Equal(t, c.String("token"), "from-plugin-token-env")

    // Reset environment
    os.Clearenv()

    // Set only TOKEN environment variable
    os.Setenv("TOKEN", "from-token-env")

    // Set without token CLI argument
    set = flag.NewFlagSet("prefer-token-env", 0)
    c = cli.NewContext(nil, set, nil)

    // TOKEN environment variable supported without token CLI argument or PLUGIN_TOKEN environment variable
    assert.Equal(t, c.String("token"), "from-token-env")

    // ...
}

[oliver-nyt]

Thanks for the comments @montmanu - i updated the docs and Makefile but still trying to get the tests to work, I don't think cli.NewContext() parses and populates the flags but trying to confirm that right now.

[oliver-nyt]

@montmanu - there more I think about these tests, the less they make sense.
This would really just tests that the library is working, none of this invokes code any plugin code
(i also still haven't figured out how to trigger env parsing of flags without using the full cli.App() thing but that's another problem)
Thoughts?

[montmanu]

i agree that its not testing much of the plugin's code, but its also a somewhat critical part of the plugin's public API, so a bit worried that from a user's e2e POV, we're not well covered on the token parsing / selection logic..

maybe it would be easier for us to figure out a way to cover that via e2e tests? build the plugin, trigger some downstream ci process that would run that version of the plugin against all versions of drone supported by the plugin?

[oliver-nyt]

Agreed this is important. Let me try something, i think i have an idea what might work.

[oliver-nyt]

Ok, I think I found a way to get the tests to do something meaningful. Might actually want to replace some others like TestCheckParams with the same App.Run() pattern to test the real plugin-code.

[tonglil]

Thanks for the changes!