Add coverify transform after command-line transforms.

If coverify runs before a transform such as [reactify](https://github.com/andreypopp/reactify), it interferes with the JSX transform resulting in failure to run the tests. Moving the converify transform later in the process fixes running test files written in JSX (via `mochify --cover --transform reactify`).

Unfortunately, this does not change the transform ordering for browserify transforms specified in `package.json`. Combining reactify (via `package.json`) and `--cover` will still fail.