Please advice how to fix following Warnings:

Please advice how to fix following Warnings:

Illegal string offset 'is_responsive' in /home/*******/public_html/wp-content/plugins/wpmu_dev_maps_plugin/inc/addons/responsive-maps.php on line 57

Warning: Illegal string offset 'is_responsive' in /home/*******/public_html/wp-content/plugins/wpmu_dev_maps_plugin/inc/addons/responsive-maps.php on line 60

Thanks