[ios][strings] Minor correction and tr string update

Signed-off-by: Alexander Borsuk <me@alex.bio>

data/strings/strings.txt

@@ -5494,7 +5494,7 @@
     sv = Donera
     sw = Changia
     th = บริจาค
-    tr = Bağış Yapın
+    tr = Bağış yapın
     uk = Підтримати грошима
     vi = Quyên tặng
     zh-Hans = 捐

iphone/Maps/Core/Settings/MWMSettings.mm

@@ -152,8 +152,7 @@ NSString * const kUDTrackWarningAlertWasShown = @"TrackWarningAlertWasShown";
 + (NSString *)donateUrl
 {
   std::string url;
-  if (settings::Get("DonateUrl", url)) return @(url.c_str());
-  return nil;
+  return settings::Get("DonateUrl", url) ? @(url.c_str()) : nil;
 }
 
 @end