vendor: bump google.golang.org/grpc v1.23.1

full diff: grpc/grpc-go@v1.23.0...v1.23.1

- grpc/grpc-go#3018 server: set and advertise max frame size of 16KB
- grpc/grpc-go#3017 grpclb: fix deadlock in grpclb connection cache
    - Before the fix, if the timer to remove a SubConn fires at the
      same time NewSubConn cancels the timer, it caused a mutex leak
      and deadlock.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

vendor.conf

@@ -79,7 +79,7 @@ golang.org/x/sys                                    6d18c012aee9febd81bbf9806760
 golang.org/x/text                                   f21a4dfb5e38f5895301dc265a8def02365cc3d0 # v0.3.0
 golang.org/x/time                                   fbb02b2291d28baffd63558aa44b4b56f178d650
 google.golang.org/genproto                          02b4e95473316948020af0b7a4f0f22c73929b0e
-google.golang.org/grpc                              6eaf6f47437a6b4e2153a190160ef39a92c7eceb # v1.23.0
+google.golang.org/grpc                              39e8a7b072a67ca2a75f57fa2e0d50995f5b22f6 # v1.23.1
 gopkg.in/inf.v0                                     d2d2541c53f18d2a059457998ce2876cc8e67cbf # v0.9.1
 gopkg.in/yaml.v2                                    bb4e33bf68bf89cad44d386192cbed201f35b241 # v2.2.3
 gotest.tools                                        1083505acf35a0bd8a696b26837e1fb3187a7a83 # v2.3.0