update vendor

Signed-off-by: Jess Frazelle <acidburn@microsoft.com>

vendor/google.golang.org/grpc/internal/envconfig/envconfig.go

@@ -0,0 +1,35 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package envconfig contains grpc settings configured by environment variables.
+package envconfig
+
+import (
+	"os"
+	"strings"
+)
+
+const (
+	prefix   = "GRPC_GO_"
+	retryStr = prefix + "RETRY"
+)
+
+var (
+	// Retry is set if retry is explicitly enabled via "GRPC_GO_RETRY=on".
+	Retry = strings.EqualFold(os.Getenv(retryStr), "on")
+)