Change Serialization of GcmNotification Priority

This fixes Redth#679 where the priority was being serialized as  a number instead of the text as per Google's docs

PushSharp.Google/GcmNotification.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.Serialization;
 using Newtonsoft.Json.Linq;
 using System.Collections.Generic;
 using PushSharp.Core;
@@ -139,7 +140,7 @@ public bool IsDeviceRegistrationIdValid ()
         /// Corresponds to iOS APNS priorities (Normal is 5 and high is 10).  Default is Normal.
         /// </summary>
         /// <value>The priority.</value>
-        [JsonProperty ("priority")]
+        [JsonProperty ("priority"), JsonConverter (typeof (Newtonsoft.Json.Converters.StringEnumConverter))]
         public GcmNotificationPriority? Priority { get; set; }
 
         internal string GetJson ()
@@ -163,7 +164,9 @@ public override string ToString ()
 
     public enum GcmNotificationPriority
     {
+        [EnumMember (Value="normal")]
         Normal = 5,
+        [EnumMember (Value="high")]
         High = 10
     }
 }

PushSharp.Tests/GcmTests.cs

@@ -0,0 +1,36 @@
+using System;
+using NUnit.Framework;
+using PushSharp.Google;
+using System.Collections.Generic;
+using Newtonsoft.Json.Linq;
+
+namespace PushSharp.Tests
+{
+    [Category ("GCM")]
+    [TestFixture]
+    public class GcmTests
+    {
+        [Test]
+        public void GcmNotification_Priority_Should_Serialize_As_String_High ()
+        {
+            var n = new GcmNotification ();
+            n.Priority = GcmNotificationPriority.High;
+
+            var str = n.ToString ();
+
+            Assert.IsTrue (str.Contains ("high"));
+        }
+
+        [Test]
+        public void GcmNotification_Priority_Should_Serialize_As_String_Normal ()
+        {
+            var n = new GcmNotification ();
+            n.Priority = GcmNotificationPriority.Normal;
+
+            var str = n.ToString ();
+
+            Assert.IsTrue (str.Contains ("normal"));
+        }
+    }
+}
+

PushSharp.Tests/PushSharp.Tests.csproj

@@ -48,6 +48,7 @@
     <Compile Include="BrokerTests.cs" />
     <Compile Include="ApnsRealTest.cs" />
     <Compile Include="WnsRealTests.cs" />
+    <Compile Include="GcmTests.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <ItemGroup>