test: make stdlib/Integer.swift.gyb python 3 friendly

Adjust the division operation to ensure that we get an integral value
back.  Without this, we would attempt to shift a floating point value
by bitwise operations which is not supported.

Author: compnerd

test/stdlib/Integers.swift.gyb

@@ -19,7 +19,8 @@
 // REQUIRES: OS=macosx
 
 %{
-word_bits = int(WORD_BITS) / 2
+from __future__ import division
+word_bits = int(WORD_BITS) // 2
 from SwiftIntTypes import all_integer_types
 }%