DOC: Fix section titles to match numpy doc standard

skimage/graph/_mcp.pyx

@@ -130,8 +130,8 @@ def make_offsets(d, fully_connected):
     -------
     offsets : list of tuples of length `d`
 
-    Example
-    -------
+    Examples
+    --------
 
     The singly-connected 2-d neighborhood is four offsets:
 

skimage/util/montage.py

@@ -45,8 +45,8 @@ def montage2d(arr_in, fill='mean', rescale_intensity=False):
         Output array where 'alpha' has been determined automatically to
         fit (at least) the `n_images` in `arr_in`.
 
-    Example
-    -------
+    Examples
+    --------
     >>> import numpy as np
     >>> from skimage.util.montage import montage2d
     >>> arr_in = np.arange(3 * 2 * 2).reshape(3, 2, 2)