Try-catch in Imagine\Gmagick\Effects::convolve should catch GmagickException instead of ImagickException

[dmitry-kulikov]

1. Try-catch in Imagine\Gmagick\Effects::convolve should catch GmagickException instead of ImagickException.
2. Changed the case of the Gmagick methods calls to lowercase to match their declarations.
3. Imagine\Test\Gmagick\EffectsTest::testColorize now expects more specific NotSupportedException instead of rather common RuntimeException.

Main reason of this pull-request is 1), it is small bugfix.
I know that tests wanted, but I'm not sure that it is required in such case because looks like its copy-paste mistake.
I tested code using the following test:
in \Imagine\Test\Gmagick\EffectsTest add

public function testConvolutionFailed()
{
    $image = $this->getImagine()->create(new \Imagine\Image\Box(1, 1));
    $matrix = new \Imagine\Utils\Matrix(3, 3, array(
        0, 0.5, 0,
        0.5, 1, 0.5,
        0, 0.5, 0,
    ));

    $this->isGoingToThrowException('Imagine\Exception\RuntimeException');
    $image->effects()->convolve($matrix);
}

then run

./vendor/bin/phpunit tests/tests/Gmagick/EffectsTest.php

Image is too small and it leads to exception. At least for
gmagick version 2.0.4RC1
GraphicsMagick version GraphicsMagick 1.3.28 2018-01-20 Q16
I'm not sure about other versions. But if gmagick will throw an exception it should be GmagickException.

[mlocati]

Thanks!