imgFormat == "RGBA" is missing.

ENV: GLPlot (0.0.3), Images (0.4.13), GLAbstraction (0.0.3)
When I try to run "image.jl" which is an example of GLPlot package, an error messages shows that "Color Format RGBA not supported".
Merge pull request #4 from kwonoh/patch-1

imgFormat == "RGBA" is missing.