doc: Trim .txt files trailing whitespace

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

doc/tut1.txt

@@ -1280,19 +1280,19 @@ with a compatible base type can be passed to an openarray parameter, the index
 type does not matter.
 
 .. code-block:: nim
-  var 
+  var
     fruits:   seq[string]       # reference to a sequence of strings that is initialized with 'nil'
     capitals: array[3, string]  # array of strings with a fixed size
-  
+
   fruits = @[]                  # creates an empty sequence on the heap that will be referenced by 'fruits'
-  
+
   capitals = ["New York", "London", "Berlin"]   # array 'capitals' allows only assignment of three elements
   fruits.add("Banana")          # sequence 'fruits' is dynamically expandable during runtime
   fruits.add("Mango")
-  
+
   proc openArraySize(oa: openArray[string]): int =
     oa.len
-  
+
   assert openArraySize(fruits) == 2     # procedure accepts a sequence as parameter
   assert openArraySize(capitals) == 3   # but also an array type