Cannot pass a random variable to TransformedDistribution

Hi,

I am using edward2==0.0.1 in combination with tensorflow_probability==0.9.0 and tensorflow==2.1.0, all installed from pip.

I am facing an issue with `ed.TransformedDistribution` that feel like a regression to me.

```python
import edward2 as ed
import tensorflow_probability as tfp
tfb = tfp.bijectors

normal = ed.Normal(0., 1.)
shifted_normal = ed.TransformedDistribution(normal, tfb.Shift(0.5))
# This raises with AttributeError: 'RandomVariable' object has no attribute 'name'
```

I can patch the case 1 by passing `normal.distribution` to `ed.TransformedDistribution` but I don't think this is desirable.