Upgrade xxhash dependency to v2.2.0 (#367)

When using ristretto in a Go plugin it's currently failing to build due
to: cespare/xxhash#54, so this PR is simply
updating the dependency.

go.mod

@@ -3,7 +3,7 @@ module github.com/dgraph-io/ristretto
 go 1.19
 
 require (
-	github.com/cespare/xxhash/v2 v2.1.1
+	github.com/cespare/xxhash/v2 v2.2.0
 	github.com/dgryski/go-farm v0.0.0-20200201041132-a6ae2369ad13
 	github.com/dustin/go-humanize v1.0.1
 	github.com/pkg/errors v0.9.1

go.sum

@@ -1,5 +1,5 @@
-github.com/cespare/xxhash/v2 v2.1.1 h1:6MnRN8NT7+YBpUIWxHtefFZOKTAPgGjpQSxqLNn0+qY=
-github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
+github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dgryski/go-farm v0.0.0-20200201041132-a6ae2369ad13 h1:fAjc9m62+UWV/WAFKLNi6ZS0675eEUC9y3AlwSbQu1Y=