fix description of 'get_activation' and some example

mindspore/nn/layer/activation.py

@@ -750,6 +750,8 @@ def get_activation(name):
 
     Examples:
         >>> sigmoid = nn.get_activation('sigmoid')
+        >>> print(sigmoid)
+        Sigmoid<>
     """
     if name is None:
         return None

mindspore/numpy/array_ops.py

@@ -2149,7 +2149,7 @@ def choose(a, choices, mode='clip'):
     Examples:
         >>> import mindspore.numpy as np
         >>> choices = [[0,   1,  2,  3], [10, 11, 12, 13],
-            [20, 21, 22, 23], [30, 31, 32, 33]]
+        ...            [20, 21, 22, 23], [30, 31, 32, 33]]
         >>> print(np.choose([2, 3, 1, 0], choices))
         [20 31 12  3]
         >>> print(np.choose([2, 4, 1, 0], choices, mode='clip'))