Fixed: test_colorspace(Image_Attributes_UT) in Image_attributes.rb fails #75

correct: sRGBColorspace (results)
incorrect: RGBColorspace (Image_attributes.rb)

> Color management has changed significantly between ImageMagick version 6.7.5-5 and 6.8.0-3 in order to better conform to color and grayscale standards.
> The first major change was to swap -colorspace RGB and -colorspace sRGB.

<cite>[ImageMagick: Color Management](http://www.imagemagick.org/script/color-management.php)</cite>

Then, I checked the Colorspace by indentify

```
C:\ruby\rmagick-2.13.3\doc\ex\images>identify -format "%[colorspace]" image_with_profile.jpg
sRGB
```