doc: Trim .txt files trailing whitespace

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

doc/spawn.txt

@@ -2,7 +2,7 @@
                   Parallel & Spawn
 ==========================================================
 
-Nim has two flavors of parallelism: 
+Nim has two flavors of parallelism:
 1) `Structured`:idx parallelism via the ``parallel`` statement.
 2) `Unstructured`:idx: parallelism via the standalone ``spawn`` statement.
 
@@ -30,7 +30,7 @@ variables at the same time:
 
 .. code-block:: nim
   import threadpool, ...
-  
+
   # wait until 2 out of 3 servers received the update:
   proc main =
     var responses = newSeq[FlowVarBase](3)
@@ -89,7 +89,7 @@ restrictions / changes:
   the ``parallel`` section. This is called the *immutability check*. Currently
   it is not specified what exactly "complex location" means. We need to make
   this an optimization!
-* Every array access has to be provably within bounds. This is called 
+* Every array access has to be provably within bounds. This is called
   the *bounds check*.
 * Slices are optimized so that no copy is performed. This optimization is not
   yet performed for ordinary slices outside of a ``parallel`` section. Slices