tests: Trim .nim files trailing whitespace

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

tests/effects/teffects3.nim

@@ -8,9 +8,9 @@ type
   TObjB = object of TObj
     a, b, c: string
     fn: proc (): int {.tags: [].}
-  
+
   EIO2 = ref object of EIO
-  
+
 proc raiser(): int {.tags: [TObj, FWriteIO].} =
   writeLine stdout, "arg"