20200802170532_fix_legacy_tags: chunk the user query

priv/repo/migrations/20200802170532_fix_legacy_tags.exs

@@ -22,7 +22,7 @@ def change do
       where: fragment("? && ?", u.tags, ^legacy_tags),
       select: struct(u, [:tags, :id])
     )
-    |> Repo.all()
+    |> Repo.chunk_stream(100)
     |> Enum.each(fn user ->
       fix_tags_changeset(user)
       |> Repo.update()