Imagick::setImageOpacity has been deprecated

[cjrasmussen]

Imagick::setImageOpacity was replaced with Imagick::setImageAlpha for ImageMagick 7. BlendableImage throws the following as a result:

Stack trace:
#0 /path/to/project/vendor/manticorp/image/src/Image.php(210): Manticorp\Image\Blender->genericBlend(0.4, 1, 'Exclusion', Array)
#1 /path/to/project/file.php(126): Manticorp\Image->blendWith(Object(Manticorp\Image), 'Exclusion', 0.4)
#2 {main}
  thrown in /path/to/project/vendor/manticorp/image/src/Image/Blender.php on line 57