Update image_similarity.py
Update image_similarity.py

Corrected one typo. If left "ANTSNeighborhoodCorrelation", the algorithm raises an error. Also, it should be corrected in the online documentation (https://antspy.readthedocs.io/en/latest/_modules/ants/utils/image_similarity.html)
ANTsX/ANTsPy,ANTsX/ANTsPy,ANTsX/ANTsPy,ANTsX/ANTsPy