Add space in 'ValueError' output.

Author: habi

skimage/measure/_regionprops.py

@@ -104,7 +104,7 @@ def __init__(self, slice, label, label_image, intensity_image,
         if intensity_image is not None:
             if not intensity_image.shape == label_image.shape:
                 raise ValueError('Label and intensity image must have the'
-                                 'same shape.')
+                                 ' same shape.')
 
         self.label = label