Fix to resolve Git Tag sorting issue #300 (#307)

* fix to resolve #300, properly sorts the tag versions returned by Git based on a 3 digit version code.  Select the actual latest version based on:

x.x.x version number

Previously, last was determined by the double value parsed value, which is incorrectly sorted by .NET.  Now sorts by each individual version identifier to locate the latest.

* Restored missing variable

XRTK-Core/Packages/com.xrtk.core/Inspectors/Utilities/Packages/MixedRealityPackageUtilities.cs

@@ -209,7 +209,8 @@ internal static async Task<Tuple<MixedRealityPackageInfo, bool>[]> GetCurrentMix
 
         private static async Task AddPackageAsync(MixedRealityPackageInfo packageInfo)
         {
-            var tag = (await GitUtilities.GetAllTagsFromRemoteAsync(packageInfo.Uri)).LastOrDefault();
+            var versionSeperator = new char[] { '.' };
+            var tag = (await GitUtilities.GetAllTagsFromRemoteAsync(packageInfo.Uri)).OrderBy(value => int.Parse(value.Split(versionSeperator)[0])).ThenBy(value => int.Parse(value.Split(versionSeperator)[1])).ThenBy(value => int.Parse(value.Split(versionSeperator)[2])).LastOrDefault();
             var addRequest = Client.Add($"{packageInfo.Name}@{packageInfo.Uri}#{tag}");
 
             await addRequest.WaitUntil(request => request.IsCompleted, timeout: 30);