Make other FormReader.ReadForm return Dictionary.

Author: Tratcher

src/Microsoft.AspNet.WebUtilities/FormReader.cs

@@ -165,7 +165,7 @@ private async Task BufferAsync(CancellationToken cancellationToken)
         /// </summary>
         /// <param name="text">The HTTP form body to parse.</param>
         /// <returns>The collection containing the parsed HTTP form body.</returns>
-        public static IDictionary<string, StringValues> ReadForm(string text)
+        public static Dictionary<string, StringValues> ReadForm(string text)
         {
             var reader = new FormReader(text);