Changing to a format string that is compatible with parse operations in Mono

Author: StanleyGoldman

src/GitHub.Api/Helpers/Constants.cs

@@ -9,7 +9,7 @@ static class Constants
         public const string UsageFile = "usage.json";
         public const string GitInstallPathKey = "GitInstallPath";
         public const string TraceLoggingKey = "EnableTraceLogging";
-        public const string Iso8601Format = "o";
+        public const string Iso8601Format = "yyyy-MM-ddTHH\\:mm\\:ss.fffffffzzz";
 
         public static readonly Version MinimumGitVersion = new Version(2, 11, 0);
         public static readonly Version MinimumGitLfsVersion = new Version(2, 3, 4);