fix: add back simple definition for internal typing

Author: Moumouls

src/SchemaMigrations/Migrations.js

@@ -1,5 +1,15 @@
 // @flow
 
+export interface SchemaOptions {
+  definitions: JSONSchema[];
+  strict: ?boolean;
+  deleteExtraFields: ?boolean;
+  recreateModifiedFields: ?boolean;
+  lockSchemas: ?boolean;
+  beforeMigration: ?() => void | Promise<void>;
+  afterMigration: ?() => void | Promise<void>;
+}
+
 export type FieldValueType =
   | 'String'
   | 'Boolean'