Fixed "Mat mask operations" tutorial. Thanks @RJ2 for pointing this.

doc/tutorials/core/mat-mask-operations/mat-mask-operations.rst

@@ -92,7 +92,7 @@ We'll use the plain C [] operator to access pixels. Because we need to access mu
        }
    }
 
-On the borders of the image the upper notation results inexistent pixel locations (like minus one - minus one). In these points our formula is undefined. A simple solution is to not apply the mask in these points and, for example, set the pixels on the borders to zeros:
+On the borders of the image the upper notation results inexistent pixel locations (like minus one - minus one). In these points our formula is undefined. A simple solution is to not apply the kernel in these points and, for example, set the pixels on the borders to zeros:
 
 .. code-block:: cpp