pkg: Rename imports after making 'pkg' a module

find -name '*.go' | xargs sed --follow-symlinks -i 's|go.etcd.io/etcd/v3/pkg/|go.etcd.io/etcd/pkg/v3/|g'
go fmt ./...

pkg/adt/README.md

@@ -16,7 +16,7 @@ For example,
 import (
     "fmt"
 
-    "go.etcd.io/etcd/v3/pkg/adt"
+    "go.etcd.io/etcd/pkg/v3/adt"
 )
 
 func main() {

pkg/adt/example_test.go

@@ -17,7 +17,7 @@ package adt_test
 import (
 	"fmt"
 
-	"go.etcd.io/etcd/v3/pkg/adt"
+	"go.etcd.io/etcd/pkg/v3/adt"
 )
 
 func Example() {