Updated Appveyor build to use Rust 1.20
Updated Appveyor build to use Rust 1.20

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