Fix MySQL migration

Author: odarriba

lib/error_tracker/migration/mysql/v04.ex

@@ -5,7 +5,7 @@ defmodule ErrorTracker.Migration.MySQL.V04 do
 
   def up(_opts) do
     alter table(:error_tracker_occurrences) do
-      add :bread_crumbs, {:array, :string}, default: [], null: false
+      add :bread_crumbs, :json, null: true
     end
   end