Fix toPreserveHook for Table[A, B]

The toPreserveHook for tables was not compiling, which would fall
back to the behavior for preserving objects, which would not work
for tables.

src/preserves.nim

@@ -574,8 +574,8 @@ proc toPreserveHook*[T](set: HashSet[T]): Preserve =
 
 proc toPreserveHook*[A, B](table: Table[A, B]|TableRef[A, B]): Preserve =
   ## Hook for preserving ``Table``.
-  result = Preserve(kind: pkDictionary, dict: initTable[Preserve, Preserve](table.len))
-  for k, v in table.pairs: result.dict.add((k.toPreserve, v.toPreserve, ))
+  result = initDictionary()
+  for k, v in table.pairs: result[k.toPreserve] = v.toPreserve
 
 proc fromPreserve*[T](v: var T; pr: Preserve): bool =
   ## Inplace version of `preserveTo`. Returns ``true`` on