Subtracting margin from BottomCenter position

Author: desmondmc

ios/RCTImageMarker/RCTImageMarker.m

@@ -244,7 +244,7 @@ void saveImageForMarker(NSString * fullPath, UIImage * image, float quality, boo
             break;
         case BottomCenter:
             posX = (w-(size.width))/2;
-            posY = h-size.height;
+            posY = h-size.height - margin;
             break;
         case BottomRight:
             posX = w-(size.width) - margin;