tests: Trim .nim files trailing whitespace

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

tests/closure/tinvalidclosure2.nim

@@ -3,12 +3,12 @@ discard """
   errormsg: "illegal capture 'A'"
 """
 
-proc outer() = 
+proc outer() =
   var A: int
 
   proc ugh[T](x: T) {.cdecl.} =
     echo "ugha", A, x
-    
+
   ugh[int](12)
 
 outer()