Update to Go 1.13 and latest dependency versions #86
Description
Go 1.13 has been released over a month ago that comes with some great features and a lot stability, performance and security improvements and bug fixes. The new os.UserConfigDir() function is a great addition for the handling for snowsaw's configuration files that will be implemented late on. See the Go 1.13 official release notes for more details.
Since there are no breaking changes snowsaw will now require Go 1.13 as minimum version.
With the update to Go 1.13.x all outdated dependencies should also be updated to their latest versions to prevent possible module incompatibilities as well as including the latest improvements and bug fixes.