Update git submodules

* Update docs/submodules/so.git from branch 'master'
  to 18bcc4e72e339aa3fb584da7799e0071151b47c2
  - Merge "Updatable to false to prevent setting fk to null"
  - Updatable to false to prevent setting fk to null
    
    Updatable to false to prevent setting foreign key to null before delete
    
    Issue-ID: SO-2178
    Signed-off-by: Benjamin, Max (mb388a) <mb388a@att.com>
    Change-Id: I9b9f94c0d0b56a61cd8b9c56e80e5a3ec4819a50
    
1 file changed