build: upgrade grpc to 1.15.0

Gopkg.lock

@@ -189,14 +189,17 @@
   revision = "a6af135bd4e28680facf08a3d206b454abc877a4"
 
 [[projects]]
-  digest = "1:19c3d5be42d5d503b94650e45bb2a01264bb36caff20f708e9cf67a6683b4c04"
+  digest = "1:52f82517e64acdc35d16c476fb8bd9191aa205eb36a450a3fc0dd5b3fe27a4ab"
   name = "github.com/golang/protobuf"
   packages = [
     "jsonpb",
     "proto",
     "protoc-gen-go/descriptor",
+    "ptypes",
     "ptypes/any",
+    "ptypes/duration",
     "ptypes/struct",
+    "ptypes/timestamp",
   ]
   pruneopts = "UT"
   revision = "bbd03ef6da3a115852eaf24c8a1c46aeb39aa175"
@@ -434,27 +437,38 @@
   revision = "df60624c1e9b9d2973e889c7a1cff73155da81c4"
 
 [[projects]]
-  digest = "1:8d9ccf0a790b530f94357a5d27e9c86fb53e862b6e0f9133c792269c0b567218"
+  digest = "1:ab8e92d746fb5c4c18846b0879842ac8e53b3d352449423d0924a11f1020ae1b"
   name = "google.golang.org/grpc"
   packages = [
     ".",
+    "balancer",
+    "balancer/base",
+    "balancer/roundrobin",
     "codes",
     "connectivity",
     "credentials",
-    "grpclb/grpc_lb_v1",
+    "encoding",
+    "encoding/proto",
     "grpclog",
     "internal",
+    "internal/backoff",
+    "internal/channelz",
+    "internal/envconfig",
+    "internal/grpcrand",
+    "internal/transport",
     "keepalive",
     "metadata",
     "naming",
     "peer",
+    "resolver",
+    "resolver/dns",
+    "resolver/passthrough",
     "stats",
     "status",
     "tap",
-    "transport",
   ]
   pruneopts = "UT"
-  revision = "b3ddf786825de56a4178401b7e174ee332173b66"
+  revision = "8dea3dc473e90c8179e519d91302d0597c0ca1d1"
 
 [[projects]]
   digest = "1:9f0c81ca4b497d3723d0a66495d8a1efe277068b77ef3ad2d6460e480bf09bb3"

Gopkg.toml

@@ -108,7 +108,7 @@
 
 [[constraint]]
   name = "google.golang.org/grpc"
-  revision = "b3ddf786825de56a4178401b7e174ee332173b66"
+  revision = "8dea3dc473e90c8179e519d91302d0597c0ca1d1"
 
 [[override]]
   name = "gopkg.in/errgo.v1"