Fix info ids.

The previous migration actually created values for the key "id", including the
quotes. This one should fill out all missing ids.

Closes #511

priv/repo/migrations/20190123125839_fix_info_ids.exs

+defmodule Pleroma.Repo.Migrations.FixInfoIds do
+  use Ecto.Migration
+
+  def change do
+    execute(
+      "update users set info = jsonb_set(info, '{id}', to_jsonb(uuid_generate_v4())) where info->'id' is null;"
+    )
+  end
+end