all: update v2 dependency

This allows us to drop the dependency on runtime/protolegacy.

Change-Id: I71e99f3759f024121244a9ef004dcdafdf1173c9
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/178543
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/go.mod b/go.mod
index c968698..95e7304 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,4 @@
 
 go 1.9
 
-require google.golang.org/protobuf v0.0.0-20190516215540-a95b29fbf623
+require google.golang.org/protobuf v0.0.0-20190522194032-21ade498bd69
diff --git a/go.sum b/go.sum
index 6876853..95906ef 100644
--- a/go.sum
+++ b/go.sum
@@ -1,10 +1,12 @@
 github.com/golang/protobuf v1.2.1-0.20190514181236-7800af189d76/go.mod h1:Zfz6qcDoDBESdv6JsKsGpgNHnkvwJAJwcA9eL+mOkgc=
 github.com/golang/protobuf v1.2.1-0.20190515194842-7574ba03306e/go.mod h1:GjgUz9uwrRQmdPBBrFqiVbojAmlpy6ryM6DCzC+20rE=
 github.com/golang/protobuf v1.2.1-0.20190516201927-a2cd3ac1b343/go.mod h1:PScGDF2x230A126tLt9Ol9RjhXzbiPJrt/CogooD2mE=
+github.com/golang/protobuf v1.2.1-0.20190516215712-ae2eaafab405/go.mod h1:UmP8hhPKR5WWIjbT9v0JEVT+U0DBSjbW8KaZVeyFfRE=
 github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 google.golang.org/protobuf v0.0.0-20190514172829-e89e6244e0e8/go.mod h1:791zQGC15vDqjpmPRn1uGPu5oHy/Jzw/Q1n5JsgIIcY=
 google.golang.org/protobuf v0.0.0-20190514231807-cdb777356907/go.mod h1:HeRLsKXv4+wE27dOIGwnqcOgq6a1O/GJ7mGhiEPnBrU=
 google.golang.org/protobuf v0.0.0-20190516201745-40b83d67fc75/go.mod h1:jf+u8AHuKtkib+0J4/bQXPNzCmT3V9a02hVzYKtatuw=
-google.golang.org/protobuf v0.0.0-20190516215540-a95b29fbf623 h1:66BSNYPKX6AuAowxFl47l/DSyZ/ZekFylmbpjDMScDQ=
 google.golang.org/protobuf v0.0.0-20190516215540-a95b29fbf623/go.mod h1:cWWmz5lsCWIcqGLROrKq5Lu231IJw2PzqOZ8cgspbfY=
+google.golang.org/protobuf v0.0.0-20190522194032-21ade498bd69 h1:C4vak6RNv+6SZeonQPm8QpfDoEd2jwk0zmv/XjuhaXc=
+google.golang.org/protobuf v0.0.0-20190522194032-21ade498bd69/go.mod h1:cJytyYi/6qdwy/+gD49hmgHcwD7zhWxE/1KPEslaZ3M=
diff --git a/internal/proto/common.go b/internal/proto/common.go
index 3e9500f..d53d2ae 100644
--- a/internal/proto/common.go
+++ b/internal/proto/common.go
@@ -13,7 +13,6 @@
 	"reflect"
 
 	"google.golang.org/protobuf/runtime/protoiface"
-	_ "google.golang.org/protobuf/runtime/protolegacy"
 )
 
 type (
diff --git a/internal/proto/registry.go b/internal/proto/registry.go
index b7ffe3d..80467ff 100644
--- a/internal/proto/registry.go
+++ b/internal/proto/registry.go
@@ -20,7 +20,6 @@
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/reflect/protoregistry"
 	"google.golang.org/protobuf/runtime/protoimpl"
-	"google.golang.org/protobuf/runtime/protolegacy"
 
 	"google.golang.org/protobuf/types/descriptorpb"
 )
@@ -317,7 +316,7 @@
 //
 // Deprecated: Use protoregistry.GlobalTypes.Register instead.
 func RegisterExtension(d *ExtensionDesc) {
-	xt := protolegacy.X.ExtensionTypeFromDesc(d)
+	xt := protoimpl.X.ExtensionTypeFromDesc(d)
 	if err := protoregistry.GlobalTypes.Register(xt); err != nil {
 		panic(err)
 	}
@@ -342,7 +341,7 @@
 		if xs == nil {
 			xs = make(extensionsByNumber)
 		}
-		xs[int32(xt.Descriptor().Number())] = protolegacy.X.ExtensionDescFromType(xt)
+		xs[int32(xt.Descriptor().Number())] = protoimpl.X.ExtensionDescFromType(xt)
 		return true
 	})