update babel-plugin-debug-macros to 0.2.0-beta.6

[kellyselden]

Mentioned here ember-cli/babel-plugin-debug-macros#69 (comment)

[rwjblue]

CI passes (which is great!), but emits a bunch of warnings to the console like this:

babel-plugin-debug-macros configuration API has changed, please update your configuration

To fix those warnings we need to tweak this section:

https://github.com/babel/ember-cli-babel/blob/8d8c5919f123073289ed31ac567e4dba8f8abddf/index.js#L246-L260

You can compare the "legacy config" test with this test in babel-plugin-debug-macros for an example.

I think we need something like:

let options = {
  externalizeHelpers: {
    global: "Ember"
  },
  debugTools: {
    isDebug: !isProduction,
    source: "@ember/debug",
    assertPredicateIndex: 1
  },
  flags: [
    {
      source: "@glimmer/env",
      flags: { DEBUG: !isProduction, CI: !!process.env.CI }
    }
  ]
};

[kellyselden]

@rwjblue I made the changes you suggested, and now everything looks good.

[rwjblue]

Looks good. Thank you!