fix(cli): flush output stream on CLI output

For some reason, this is now a requirement - previously this didn't
seem to be necessary.

Don't know what changed there ... and it's odd it doesn't flush
when the process is going down or the handle is destroyed.

src/mako/cli/lib/engine.mako

@@ -326,13 +326,15 @@ if dry_run {
             let mut value = json::value::to_value(&output_schema);
             remove_json_null_values(&mut value);
             json::to_writer_pretty(&mut ostream, &value).unwrap();
+            ostream.flush().unwrap();
             % endif
             % if track_download_flag:
             } else {
             % endif
             % if supports_media_download:
             ## Download is the only option - nothing else matters
             io::copy(&mut response, &mut ostream).unwrap();
+            ostream.flush().unwrap();
             % endif
             % if track_download_flag:
             }