Flush ProcessUtil buffer (#952)

* Update ProcessUtil.cs

* Update ProcessUtil.cs

src/Microsoft.Tye.Core/ProcessUtil.cs

@@ -103,6 +103,10 @@ namespace Microsoft.Tye
 
             process.Exited += (_, e) =>
             {
+                // Even though the Exited event has been raised, WaitForExit() must still be called to ensure the output buffers
+                // have been flushed before the process is considered completely done.
+                process.WaitForExit();
+
                 if (throwOnError && process.ExitCode != 0)
                 {
                     processLifetimeTask.TrySetException(new InvalidOperationException($"Command {filename} {arguments} returned exit code {process.ExitCode}"));