fix string extensions

Author: jaredcnance

JsonApiDotNetCore/Extensions/StringExtensions.cs

@@ -21,8 +21,19 @@ public static string ToProperCase(this string str)
       var chars = str.ToCharArray();
       if (chars.Length > 0)
       {
-        chars[0] = new string(chars[0], 1).ToUpper().ToCharArray()[0];
-        return new String(chars);
+        chars[0] = char.ToUpper(chars[0]);
+        var builder = new StringBuilder();
+        for(var i = 0; i  < chars.Length; i++)
+        {
+          if((chars[i]) == '-') {
+            i = i + 1;
+            builder.Append(char.ToUpper(chars[i]));
+          }
+          else {
+            builder.Append(chars[i]);
+          }
+        }
+        return builder.ToString();
       }
       return str;
     }

JsonApiDotNetCoreTests/Extensions/UnitTests/StringExtensionsTests.cs

@@ -19,6 +19,7 @@ public void ToCamelCase_ConvertsString_ToCamelCase(string input, string expected
 
         [Theory]
         [InlineData("todoItem", "TodoItem")]
+        [InlineData("todo-items", "TodoItems")]
         public void ToProperCase_ConvertsString_ToProperCase(string input, string expectedOutput)
         {
             // arrange