return nil from assignment benchmarks

Author: Charlie Somerville

code/general/assignment.rb

@@ -2,6 +2,7 @@
 
 def slow
   a, b, c, d, e, f, g, h = 1, 2, 3, 4, 5, 6, 7, 8
+  nil
 end
 
 def fast
@@ -13,6 +14,7 @@ def fast
   f = 6
   g = 7
   h = 8
+  nil
 end
 
 Benchmark.ips do |x|