Adaptive image Fatal error: [] operator not supported for strings

Hi all.

I've encountered an error while using the Bootstrap module and have traced it back to adatptive_image

on Line 201 it's currently: $variables['attributes']['class'] = 'adaptive-image';

This code overrides the values from other modules. It should be declared as an array. eg. $variables['attributes']['class'][] = 'adaptive-image';