Added Pinterest as a BranchActivityItemProvider channel.

Author: E-B-Smith

Branch-SDK/Branch-SDK/BranchActivityItemProvider.m

@@ -93,6 +93,7 @@ + (NSString *)humanReadableChannelWithActivityType:(NSString *)activityString {
         @"WhatsApp", @"net.whatsapp.WhatsApp.ShareExtension",
         @"WeChat", @"com.tencent.xin.sharetimeline",
         @"LINE", @"jp.naver.line.Share",
+		@"Pinterest", @"pinterest.ShareExtension",
         nil
     ];
     // Set to a more human readible sting if we can identify it