Fix markup.

Doc/library/itertools.rst

@@ -760,7 +760,7 @@ which incur interpreter overhead.
 
 Note, many of the above recipes can be optimized by replacing global lookups
 with local variables defined as default values.  For example, the
-*dotproduct* recipe can be written as:
+*dotproduct* recipe can be written as::
 
    def dotproduct(vec1, vec2, sum=sum, imap=imap, mul=operator.mul):
        return sum(imap(mul, vec1, vec2))