dump-dir and dump options were remove somewhere in version 7.x https://github.com/drush-ops/drush/commit/df3980062a89436a26db20097363da69616cbb9c

You can still find it in 6.x branch but not in 8.x https://github.com/drush-ops/drush/blob/6.x/examples/example.aliases.drushrc.php

In issue https://github.com/drush-ops/drush/issues/1495 you can read:

markcarver: What happened to drush_sql_dump_file()?

 

weitzman: The feature is gone. sql-sync does not keep around transferred dump files any more.

dump-dir and dump options were remove somewhere in version 7.x https://github.com/drush-ops/drush/commit/df3980062a89436a26db20097363da69616cbb9c

You can still find it in 6.x branch but not in 8.x https://github.com/drush-ops/drush/blob/6.x/examples/example.aliases.drushrc.php

In issue https://github.com/drush-ops/drush/issues/1495 you can read:

markcarver: What happened to drush_sql_dump_file()?

weitzman: The feature is gone. sql-sync does not keep around transferred dump files any more.