Fix color for clear mask type

Author: jcgsxr

Demo/WSProgressHUD.xcodeproj/project.xcworkspace/contents.xcworkspacedata

@@ -982,7 +982,7 @@ - (void)drawRect:(CGRect)rect
     switch (self.maskType) {
         case WSProgressHUDMaskTypeClear: {
             CGContextRef context = UIGraphicsGetCurrentContext();
-            [[UIColor colorWithWhite:0 alpha:0.5] set];
+			[[UIColor clearColor] set];
             CGRect bounds = self.bounds;
             CGContextFillRect(context, bounds);
         }break;