Merge tag 'v1.1.5'

1.1.5

 * Add contribution guidelines (Ryan Graham)
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