tests: Trim .nim files trailing whitespace

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

tests/effects/teffects1.nim

@@ -7,11 +7,11 @@ type
   TObj = object {.pure, inheritable.}
   TObjB = object of TObj
     a, b, c: string
-  
+
   IO2Error = ref object of IOError
-  
+
 proc forw: int {. .}
-  
+
 proc lier(): int {.raises: [IO2Error].} =
   writeLine stdout, "arg"