Update middleware.go

[alexbowers]

Before these changes, compiling myself I would get:

go: downloading github.com/throttled/throttled v1.0.0
go: downloading github.com/throttled/throttled/v2 v2.7.1
go: downloading github.com/throttled/throttled v2.2.5+incompatible
go get: gopkg.in/throttled/[email protected] updating to
	gopkg.in/throttled/[email protected]: parsing go.mod:
	module declares its path as: github.com/throttled/throttled/v2
	        but was required as: gopkg.in/throttled/throttled.v2