v3.1.0

• new: .npmignore tests
• fix: validate requested scope on authorize request
• fix: always issue correct expiry dates for tokens
• fix: set numArgs for promisify of generateAuthorizationCode
• fix: Changed 'hasOwnProperty' call in Response
• docs: Ensure accessTokenExpiresAt is required
• docs: Add missing notice of breaking change for accessExpireLifetime to migration guide
• docs: Correct tokens time scale for 2.x to 3.x migration guide
• readme: Update Slack badge and link
• readme: Fix link to RFC6750 standard