Update docstring to match broadcasting results

In ce9c17f3 the RV was changed such that `p` can be multi-dimensional instead of just 1-dimensional. Since then the support length is determined by the last dimension of `p`.

Update docstring to match broadcasting results
89a67964 · Michael Osthege · Thomas Wiecki · 2d3cb775 · 89a67964
--- a/aesara/tensor/random/basic.py
+++ b/aesara/tensor/random/basic.py
@@ -492,8 +492,8 @@ betabinom = BetaBinomialRV()
 class MultinomialRV(RandomVariable):
    """A Multinomial random variable type.
-    FYI: Support shape is determined by the first dimension in the *second*
+    FYI: Length of the support dimension is determined by the last
-    parameter (i.e.  the probabilities vector).
+    dimension in the *second* parameter (i.e.  the probabilities vector).
    """