update changelog for release 0.8.4
update changelog for release 0.8.4

pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference