(GH-455) Adjust summary for unfound sources

Update the summary when warning about unfound sources so that only the
first sentence is shown in the package warning summary. This reduces
the amount of text seen in the summary.

src/chocolatey/infrastructure.app/services/NugetService.cs

@@ -602,7 +602,7 @@ public ConcurrentDictionary<string, PackageResult> upgrade_run(ChocolateyConfigu
                     }
                     else
                     {
-                        unfoundResult.Messages.Add(new ResultMessage(ResultType.Warn, logMessage));
+                        unfoundResult.Messages.Add(new ResultMessage(ResultType.Warn, "{0} was not found with the source(s) listed.".format_with(packageName)));
                         unfoundResult.Messages.Add(new ResultMessage(ResultType.Inconclusive, logMessage));
                         if (config.RegularOutput)
                         {