fix README so travis status points to JuliaGPU organization
fix README so travis status points to JuliaGPU organization

yuyichao/OpenCL.jl,tkelman/OpenCL.jl,yuyichao/OpenCL.jl,JuliaPackageMirrors/OpenCL.jl,JuliaPackageMirrors/OpenCL.jl,tkelman/OpenCL.jl