add webp format to image extensions
add webp format to image extensions

JordanReiter/sorl-thumbnail,JordanReiter/sorl-thumbnail,gregplaysguitar/sorl-thumbnail,jannon/sorl-thumbnail,gregplaysguitar/sorl-thumbnail,JordanReiter/sorl-thumbnail,gregplaysguitar/sorl-thumbnail,jazzband/sorl-thumbnail,jannon/sorl-thumbnail,jazzband/sorl-thumbnail,jazzband/sorl-thumbnail,mariocesar/sorl-thumbnail,mariocesar/sorl-thumbnail,mariocesar/sorl-thumbnail,jannon/sorl-thumbnail