Add go modules for go version 1.17

go.mod

@@ -0,0 +1,25 @@
+module github.com/GoogleCloudPlatform/docker-credential-gcr
+
+go 1.17
+
+require (
+	github.com/docker/cli v20.10.8+incompatible
+	github.com/docker/docker-credential-helpers v0.6.4
+	github.com/golang/mock v1.6.0
+	github.com/google/subcommands v1.2.0
+	github.com/toqueteos/webbrowser v1.2.0
+	golang.org/x/oauth2 v0.0.0-20210819190943-2bc19b11175f
+)
+
+require (
+	cloud.google.com/go v0.65.0 // indirect
+	github.com/docker/docker v20.10.8+incompatible // indirect
+	github.com/golang/protobuf v1.4.2 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/sirupsen/logrus v1.8.1 // indirect
+	golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4 // indirect
+	golang.org/x/sys v0.0.0-20210510120138-977fb7262007 // indirect
+	google.golang.org/appengine v1.6.6 // indirect
+	google.golang.org/protobuf v1.25.0 // indirect
+	gotest.tools/v3 v3.0.3 // indirect
+)