tests: Trim .nim files trailing whitespace

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

tests/objects/toop.nim

@@ -5,13 +5,13 @@ discard """
 type
   TA = object of TObject
     x, y: int
-  
+
   TB = object of TA
     z: int
-    
+
   TC = object of TB
     whatever: string
-  
+
 proc p(a: var TA) = echo "a"
 proc p(b: var TB) = echo "b"