0.21.0

• #265, #278, #279, #280 Add support for new correlation headers and exporting custom properties cross-server
• #271 Update travis ci definitions
• #274 Fix trackDependency serialization when used with fractional milliseconds
• #272 Clear all usages of implicit any
• #276 Update diagnostic-channel-publishers to 0.1.3
• #277 Fix flaky unit test failures