Add cordova-plugin-test-framework as dependency of plugin tests?

README says:

> Q: Should I add cordova-plugin-test-framework as a of my plugin?
> A: No. The end-user should decide if they want to install the test framework, not your plugin (most users won't).

But you could probably add this as a dependency for the tests themselves, so when a user installs the tests "plugin", this comes with it and the tests can automatically be run (instead of requiring a manual install of `cordova-plugin-test-framework`)