4.1.0

• [browser] feat: Better mechanism detection in TraceKit
• [browser] fix: Change loader to use getAttribute instead of dataset
• [browser] fix: Remove trailing commas from loader for IE10/11
• [browser] ref: Include md5 lib and transcript it to TypeScript
• [browser] ref: Remove all trailing commas from integration tests cuz IE10/11
• [browser] ref: Remove default transaction from browser
• [browser] ref: Remove redundant debug.ts file from browser integrations
• [browser] test: Fix all integration tests in IE10/11 and Android browsers
• [browser] test: Run integration tests on SauceLabs
• [browser] test: Stop running raven-js saucelabs tests in favour of @sentry/browser
• [browser] test: Store breadcrumbs in the global variable in integration tests
• [browser] test: Update polyfills for integration tests
• [build] ref: Use Mocha v4 instead of v5, as it's not supporting IE10
• [core] feat: Introduce stringify and debugger options in Debug integration
• [core] feat: RewriteFrames pluggable integration
• [core] feat: getRequestheaders should handle legacy DSNs
• [core] fix: correct sampleRate behaviour
• [core] misc: Warn user when beforeSend doesnt return an event or null
• [core] ref: Check for node-env first and return more accurate global object
• [core] ref: Remove Repo interface and repos attribute from Event
• [core] ref: Rewrite RequestBuffer using Array instead of Set for IE10/11
• [hub] fix: Scope level overwrites level on the event
• [hub] fix: Correctly store and retrieve Hub from domain when one is active
• [hub] fix: Copy over user data when cloning scope
• [node] feat: Allow requestHandler to be configured
• [node] feat: Allow pick any user attributes from requestHandler
• [node] feat: Make node transactions a pluggable integration with tests
• [node] feat: Transactions handling for RequestHandler in Express/Hapi
• [node] fix: Dont wrap native modules more than once to prevent leaks
• [node] fix: Add the same protocol as dsn to base transport option
• [node] fix: Use getCurrentHub to retrieve correct hub in requestHandler
• [utils] ref: implemented includes, assign and isNaN polyfills