Rename updateBoardEpicUserPref to snake_case

ee/app/assets/javascripts/boards/stores/actions.js

@@ -40,7 +40,7 @@ import issueSetWeightMutation from '../graphql/issue_set_weight.mutation.graphql
 import listUpdateLimitMetricsMutation from '../graphql/list_update_limit_metrics.mutation.graphql';
 import listsEpicsQuery from '../graphql/lists_epics.query.graphql';
 import projectBoardMilestonesQuery from '../graphql/project_board_milestones.query.graphql';
-import updateBoardEpicUserPreferencesMutation from '../graphql/updateBoardEpicUserPreferences.mutation.graphql';
+import updateBoardEpicUserPreferencesMutation from '../graphql/update_board_epic_user_preferences.mutation.graphql';
 
 import boardsStoreEE from './boards_store_ee';
 import * as types from './mutation_types';