tests: Trim .nim files trailing whitespace

via OSX: find . -name '*.nim' -exec sed -i '' -E 's/[[:space:]]+$//' {} +

tests/parallel/treadafterwrite.nim

@@ -12,7 +12,7 @@ type
   BoxedFloat = object
     value: float
 
-proc term(k: float): ptr BoxedFloat = 
+proc term(k: float): ptr BoxedFloat =
   var temp = 4 * math.pow(-1, k) / (2*k + 1)
   result = cast[ptr BoxedFloat](allocShared(sizeof(BoxedFloat)))
   result.value = temp