Update appveyor build to use Rust 1.16.0
Update appveyor build to use Rust 1.16.0

pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,AssafKatz3/pact-reference,pact-foundation/pact-mock-server,AssafKatz3/pact-reference,pact-foundation/pact-reference,AssafKatz3/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,pact-foundation/pact-reference,AssafKatz3/pact-reference,pact-foundation/pact-reference