Updating parallell computing text

Behaviour was not as documented.

doc/manual/parallel-computing.rst

@@ -141,13 +141,10 @@ type the following into the Julia prompt::
  0.153756 0.368514
  1.15119 0.918912
 
- julia> @spawn rand2(2,2)
- Future(2,1,4,Nullable{Any}())
-
- julia> @spawn rand2(2,2)
- Future(3,1,5,Nullable{Any}())
+ julia> fetch(@spawn rand2(2,2))
+ ERROR: On worker 2:
+ function rand2 not defined on process 2
 
- julia> exception on 2: in anonymous: rand2 not defined
 
 Process 1 knew about the function ``rand2``, but process 2 did not.