Update hierarchical.rst: minor fix to hierarchical example

docs/hierarchical.rst

@@ -230,7 +230,6 @@ uses the default nested sampling routine to draw the samples from :math:`\mu`.
 
    # set the sampler keyword arguments
    sampler_kwargs = {
-       "sample": "unif",
        "nlive": 500,
        "gzip": True,
        "outdir": "exponential_distribution",
@@ -249,7 +248,7 @@ uses the default nested sampling routine to draw the samples from :math:`\mu`.
    )
 
    # run the sampler
-   res = mqd.sample()
+   res = mqd.sample(sample="unif")
 
 The ``res`` value returned by :meth:`~cwinpy.hierarchical.MassQuadrupoleDistribution.sample` will be
 a :class:`~bilby.core.result.Result` object containing the posterior samples for :math:`\mu`.
@@ -648,4 +647,4 @@ Hierarchical analysis references
    **98**, 063001 (2018).
 .. [3] `D. W. Hogg, A. D. Myers & J. Bovy
    <https://ui.adsabs.harvard.edu/abs/2010ApJ...725.2166H/abstract>`_, *ApJ*,
-   **725**,  2166-2175 (2010).
\ No newline at end of file
+   **725**,  2166-2175 (2010).