Bump Golang 1.13.9
go1.13.9 (released 2020/03/19) includes fixes to the go command, tools, the
runtime, the toolchain, and the crypto/cypher package. See the Go 1.13.9
milestone on the issue tracker for details:
https://github.com/golang/go/issues?q=milestone%3AGo1.13.9+label%3ACherryPickApproved
full diff: https://github.com/golang/go/compare/go1.13.8...go1.13.9
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>