Ensure the final span is shipped to jaeger before exiting.

src/main.rs

@@ -12,6 +12,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let parsed = document(TEST_DOC);
     println!("{}\n\n\n", TEST_DOC);
     println!("{:#?}", parsed);
+    opentelemetry::global::shutdown_tracer_provider();
     Ok(())
 }