add a no-op optimization

[kellyselden]

Closes #201

[stefanpenner]

@kellyselden I like this, but can you add a quick unit test for that hook, ensuring that this works as expected (and continues to into the future)

[kellyselden]

@stefanpenner added a test

[rwjblue]

looks good, can you add a test that roughly does:

        subject = this.addon.transpileTree(input.path(), {
          'ember-cli-babel': {
            compileModules: false,
            disablePresetEnv: true,
            disableDebugTooling: true,
            disableEmberModulesAPIPolyfill: true
          }
        });

         expect(subject).to.equal(input.path());

[kellyselden]

@rwjblue That's essentially what my test is. What would you like changed?

[stefanpenner]

released as v6.12.0 🎉