update changelog for release 0.7.15
update changelog for release 0.7.15

pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-mock-server,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference