Make likelihood condition strictly increasing

There's a bug in the acceptance condition used in dynesty, see https://github.com/joshspeagle/dynesty/pull/203.

This fixes our walk function.

bilby/core/sampler/dynesty.py

@@ -756,7 +756,7 @@ def sample_rwalk_bilby(args):
         # Check proposed point.
         v_prop = prior_transform(np.array(u_prop))
         logl_prop = loglikelihood(np.array(v_prop))
-        if logl_prop >= loglstar:
+        if logl_prop > loglstar:
             u = u_prop
             v = v_prop
             logl = logl_prop