Update to use go modules (#671)

This includes updates to CI config, vendor files, etc.
I've hard-coded the k8s depedency at 1.13.4 to keep it inline with what
we currently have and to make sure a another run of `go mod tidy`
doesn't accidentally update it to an unexpected version.

Thanks to hectorj2f for carrying this along.

vendor/github.com/json-iterator/go/reflect_extension.go

@@ -338,7 +338,7 @@ func describeStruct(ctx *ctx, typ reflect2.Type) *StructDescriptor {
 	for i := 0; i < structType.NumField(); i++ {
 		field := structType.Field(i)
 		tag, hastag := field.Tag().Lookup(ctx.getTagKey())
-		if ctx.onlyTaggedField && !hastag {
+		if ctx.onlyTaggedField && !hastag && !field.Anonymous() {
 			continue
 		}
 		tagParts := strings.Split(tag, ",")