fix typo

Author: mythz

src/ServiceStack.Text/StringExtensions.cs

@@ -919,7 +919,7 @@ public static IEnumerable<string> ReadLines(this string text)
             }
         }
 
-        public static int CountOccurancesOf(this string text, char needle)
+        public static int CountOccurrencesOf(this string text, char needle)
         {
             var chars = text.ToCharArray();
             var count = 0;