Fall back to default upsert implementation

See:
https://github.com/strongloop/loopback-connector-postgresql/issues/27
https://github.com/strongloop/loopback-connector-postgresql/pull/40
Merge pull request #41 from strongloop/feature/fix-issue-27

Fall back to default upsert implementation
Bump version
Merge branch 'release/1.2.0' into production
Merge tag 'v1.2.0'

1.2.0