Add go modules and update cli flag creation to work with latest urfave/cli changes

go.mod

@@ -0,0 +1,33 @@
+module github.com/segmentio/envoy-consul-sds
+
+go 1.12
+
+require (
+	github.com/armon/go-metrics v0.3.0 // indirect
+	github.com/gin-contrib/sse v0.1.0 // indirect
+	github.com/gin-gonic/gin v1.4.0
+	github.com/golang/protobuf v1.3.2 // indirect
+	github.com/google/btree v1.0.0 // indirect
+	github.com/hashicorp/consul/api v1.3.0
+	github.com/hashicorp/go-immutable-radix v1.1.0 // indirect
+	github.com/hashicorp/go-msgpack v0.5.5 // indirect
+	github.com/hashicorp/go-rootcerts v1.0.1 // indirect
+	github.com/hashicorp/go-sockaddr v1.0.2 // indirect
+	github.com/hashicorp/golang-lru v0.5.3 // indirect
+	github.com/hashicorp/memberlist v0.1.5 // indirect
+	github.com/hashicorp/serf v0.8.5 // indirect
+	github.com/json-iterator/go v1.1.8 // indirect
+	github.com/kr/pretty v0.1.0 // indirect
+	github.com/mattn/go-isatty v0.0.10 // indirect
+	github.com/miekg/dns v1.1.22 // indirect
+	github.com/pkg/errors v0.8.1
+	github.com/stretchr/testify v1.4.0 // indirect
+	github.com/ugorji/go/codec v1.1.7 // indirect
+	github.com/urfave/cli v1.22.1
+	golang.org/x/crypto v0.0.0-20191112222119-e1110fd1c708 // indirect
+	golang.org/x/net v0.0.0-20191112182307-2180aed22343 // indirect
+	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e // indirect
+	golang.org/x/sys v0.0.0-20191112214154-59a1497f0cea // indirect
+	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
+	gopkg.in/yaml.v2 v2.2.5 // indirect
+)