Parse error : syntax error, unexpected ‘)’ in

You have a missing closing bracket on your params parameter on the array_merge(). It should look like this:

    return array(
        'name' => __('Custom Fields', 'thegem'),
        'base' => 'gem_custom_fields',
        'icon' => 'thegem-icon-wpb-ui-custom-fields',
        'category' => __('TheGem', 'thegem'),
        'description' => __('Custom Fields', 'thegem'),
        'params' => array_merge(
            /* General - Layout */
            thegem_cf_set_layout_params(),

            /* General - Styles */
            thegem_cf_set_style_params(),

            /* Extra Options */
            thegem_set_elements_extra_options(),

            // Design Options
            thegem_cf_set_design_options_params(),

            /* Responsive Options */
            thegem_set_elements_responsive_options(),
            thegem_cf_extends_responsive_options_params(),
         ) // <-- missing this bracket
     ); // <-- missing semicolon