corrected typo

Author: gertingold

presentation.pdf

@@ -598,7 +598,7 @@
  \begin{enumerate}
   \item The arrays all have exactly the same shape.
   \item The arrays all have the same number of dimensions and the
-        length of each dimensions is either a common length or 1.
+        length of each dimension is either a common length or 1.
   \item The arrays that have too few dimensions can have their
         shapes prepended with a dimension of length 1 to satisfy
         property 2.