lib/db: Add Badger backend (fixes #5910) (#6250)

go.mod

@@ -10,6 +10,7 @@ require (
 	github.com/certifi/gocertifi v0.0.0-20190905060710-a5e0173ced67 // indirect
 	github.com/chmduquesne/rollinghash v0.0.0-20180912150627-a60f8e7142b5
 	github.com/d4l3k/messagediff v1.2.1
+	github.com/dgraph-io/badger/v2 v2.0.3
 	github.com/flynn-archive/go-shlex v0.0.0-20150515145356-3f9db97f8568
 	github.com/getsentry/raven-go v0.2.0
 	github.com/go-ldap/ldap/v3 v3.1.10
@@ -45,7 +46,6 @@ require (
 	golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae
 	golang.org/x/text v0.3.2
 	golang.org/x/time v0.0.0-20190308202827-9d24e82272b4
-	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 )
 
 go 1.13