Git Client comparison fix

Author: StanleyGoldman

src/GitHub.Api/Git/GitClient.cs

@@ -119,7 +119,7 @@ private Task<NPath> LookForPortableGit()
             var searchPath = "PortableGit_";
 
             var portableGitPath = gitHubLocalAppDataPath.Directories()
-                .Where(s => s.FileName.StartsWith(searchPath, StringComparison.InvariantCultureIgnoreCase))
+                .Where(s => s.FileName.StartsWith(searchPath, StringComparison.OrdinalIgnoreCase))
                 .FirstOrDefault();
 
             if (portableGitPath != null)