Fix GL.Target rasterization for Retina screens. Fix #4

RNGL/GLTexture.m

 #import "GLTexture.h"
 #import "RCTLog.h"
+#import "RCTUtils.h"
 
 GLImageData* genPixelsEmpty (int width, int height)
 {
@@ -53,13 +54,14 @@ GLImageData* genPixelsWithImage (UIImage *image)
 
 GLImageData* genPixelsWithView (UIView *view)
 {
-  int width = view.bounds.size.width;
-  int height = view.bounds.size.height;
+  float width = RCTScreenScale() * view.bounds.size.width;
+  float height = RCTScreenScale() * view.bounds.size.height;
   GLubyte *data = (GLubyte *)malloc(4 * width * height);
   CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
   CGContextRef ctx = CGBitmapContextCreate(data, width, height, 8, 4 * width, colourSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
   CGColorSpaceRelease(colourSpace);
-  CGContextClearRect(ctx, view.bounds);
+  CGContextClearRect(ctx, CGRectMake(0.0, 0.0, width, height));
+  CGContextScaleCTM(ctx, RCTScreenScale(), RCTScreenScale());
   [view.layer renderInContext:ctx];
   CGContextRelease(ctx);
   return [[GLImageData alloc] initWithData:data withWidth:width withHeight:height];