Update git submodules

* Update docs/submodules/policy/engine.git from branch 'master'
  to 51d9bb17422ae08042971e9cb87bd6a2576a5cdb
  - Unit/SONAR/Checkstyle in ONAP-REST
    
    Util package of ONAP-REST, with JUnit added and
    SONAR/Checkstyle issues addressed. Coverage increased from 51% to 73% in
    large PolicyValidation class.
    
    Issue-ID: POLICY-2131
    Change-Id: Iffa90e2dfa155d3e9cac114032fb9ca0df2cbab0
    Signed-off-by: liamfallon <liam.fallon@est.tech>
    
1 file changed