tests: Trim .nim files trailing whitespace

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

tests/effects/teffects2.nim

@@ -7,9 +7,9 @@ type
   TObj = object {.pure, inheritable.}
   TObjB = object of TObj
     a, b, c: string
-  
+
   EIO2 = ref object of IOError
-  
+
 proc forw: int {.raises: [].}
 
 proc lier(): int {.raises: [IOError].} =