Bug Description

The uniform probability density function (numpyro.distributions.Uniform) gives a non-zero probability density for events outside of its support. That is, if we define the density $p(x) = U(x \mid a,b)$, with $a$ and $b$ its lower and upper bounds, then $p(x)$ should be zero for $x\not\in [a,b]$.

Steps to Reproduce

import numpyro.distributions as dist
assert jnp.exp(dist.Uniform(0.0, 5.0).log_prob(7.0)) == 0.0

Expected Behavior

For values of $x$ outside of the support, uniform.log_prob() should return -inf.