eslintrc: extend recommended configuration of flowtype plugin
eslintrc: extend recommended configuration of flowtype plugin

Previously it was in the section for customized rules, but not rules
were specified, resulting in this not taking any effect.

cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit