Fix canonical package name of the bbolt package

This is a very indirect dependency, via eirinix, cobra, viper, etcd. The
initial problem is in etcd-v3.3, with an incorrect import of
github.com/coreos/bbolt. This is fixed in etcd-v3.4, however, etcd-v3.4
is not a correct go module, and cannot be included in a go mod project!
So everyone must wait for etcd-v3.5 to be released with the fix. See
etcd-io/etcd#11154 (comment).

Until then, we can rename bbolt. Fixing to v1.3.5 is unfortunately
required by go.mod's syntax. It should be upgraded if bbolt releases
again.

Signed-off-by: Danail Branekov <danailster@gmail.com>

go.mod

@@ -3,6 +3,7 @@ module code.cloudfoundry.org/eirini
 go 1.13
 
 replace (
+	github.com/coreos/bbolt => go.etcd.io/bbolt v1.3.5
 	github.com/go-logr/logr => github.com/go-logr/logr v0.1.0
 	github.com/googleapis/gnostic => github.com/googleapis/gnostic v0.4.0
 	k8s.io/client-go => k8s.io/client-go v0.18.6