Strip punctuation from attribution (#3287)

platform/darwin/src/MLNAttributionInfo.mm

@@ -104,9 +104,13 @@
             [attributedString removeAttribute:NSStrokeWidthAttributeName range:range];
         }
 
-        // Omit whitespace-only strings.
+        // Clean up strings by stripping punctuation and whitespace (often present for the web).
+        NSMutableCharacterSet *charset = [NSMutableCharacterSet whitespaceAndNewlineCharacterSet];
+        [charset formUnionWithCharacterSet:[NSCharacterSet punctuationCharacterSet]];
         NSAttributedString *title = [[attributedString attributedSubstringFromRange:range]
-                                     mgl_attributedStringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
+                                     mgl_attributedStringByTrimmingCharactersInSet:charset];
+
+        // Omit strings that are empty after cleaning.
         if (!title.length) {
             return;
         }

platform/darwin/test/MLNAttributionInfoTests.m

@@ -20,7 +20,7 @@
 - (void)testParsing {
     static NSString * const htmlStrings[] = {
         @"<a href=\"https://www.mapbox.com/about/maps/\" target=\"_blank\">&copy; Mapbox</a> "
-        @"<a href=\"http://www.openstreetmap.org/about/\" target=\"_blank\">©️ OpenStreetMap</a> "
+        @"<a href=\"http://www.openstreetmap.org/about/\" target=\"_blank\">©️ OpenStreetMap</a>, "
         @"CC&nbsp;BY-SA "
         @"<a class=\"mapbox-improve-map\" href=\"https://apps.mapbox.com/feedback/\" target=\"_blank\">Improve this map</a>",
     };