message: fix random uniform problem
  The bug occurs when minval equals maxval.
diff: @@ -1188,6 +1188,9 @@ def random_normal_variable(shape, mean, scale, dtype=None, name=None, seed=None)
  def random_uniform(shape, minval=0.0, maxval=1.0, dtype=None, seed=None):
  + if minval == maxval:
  + return constant(minval, dtype, shape)
  +
  dtype = dtype or floatx()
  rng_state = _make_rng_state(seed)
  shape_inputs = []
  