fix(ios): Fix image size when calling getDataURL with bounds. fixes #855

UIGraphicsBeginImageContextWithOptions third argument was incorrect:

https://developer.apple.com/documentation/uikit/1623912-uigraphicsbeginimagecontextwitho
The scale factor to apply to the bitmap. If you specify a value of 0.0,
the scale factor is set to the scale factor of the device’s main screen.

ios/Elements/RNSVGSvgView.m

@@ -268,7 +268,7 @@ - (NSString *)getDataURL
 
 - (NSString *)getDataURLwithBounds:(CGRect)bounds
 {
-    UIGraphicsBeginImageContextWithOptions(bounds.size, NO, 0);
+    UIGraphicsBeginImageContextWithOptions(bounds.size, NO, 1);
     [self clearChildCache];
     [self drawRect:bounds];
     [self clearChildCache];