[ci] rails 5: Fix ruby 2.0 parser error reported by rubocop

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spec/controllers/webui/user_controller_spec.rb:101:43: E: unexpected token tCOLON
(Using Ruby 2.0 parser; configure using TargetRubyVersion parameter, under AllCops)
      expect(response.body).to eq({"sEcho": 2, "iTotalRecords": 1, "iTotalDisplayRecords": 1, "aaData": []}.to_json)