tests: Trim .nim files trailing whitespace

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

tests/closure/tnestedproc.nim

@@ -2,10 +2,10 @@ discard """
   output: "11"
 """
 
-proc p(x, y: int): int = 
+proc p(x, y: int): int =
   result = x + y
 
-echo p((proc (): int = 
+echo p((proc (): int =
           var x = 7
           return x)(),
        (proc (): int = return 4)())