nix: Add protoc-gen-go-grpc package

This command is used in `go generate` but hadn't been pulled into the
nix dependencies yet. Previously I was installing the binary via `go
get` but this is cleaner and more nix-y.

Also includes a `nix flake update` for good measure.

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "flake-utils": {
       "locked": {
-        "lastModified": 1634851050,
-        "narHash": "sha256-N83GlSGPJJdcqhUxSCS/WwW5pksYf3VP1M13cDRTSVA=",
+        "lastModified": 1644229661,
+        "narHash": "sha256-1YdnJAsNy69bpcjuoKdOYQX0YxZBiCYZo4Twxerqv7k=",
         "owner": "numtide",
         "repo": "flake-utils",
-        "rev": "c91f3de5adaf1de973b797ef7485e441a65b8935",
+        "rev": "3cecb5b042f7f209c56ffd8371b2711a290ec797",
         "type": "github"
       },
       "original": {
@@ -17,11 +17,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1636678824,
-        "narHash": "sha256-NDB9CenPn5z2xbmG/X+Mg6Jd8iUEf7dfprQfXxSD6X8=",
+        "lastModified": 1645937171,
+        "narHash": "sha256-n9f9GZBNMe8UMhcgmmaXNObkH01jjgp7INMrUgBgcy4=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "bf346b557b76ffce74167f37752656dede5957f3",
+        "rev": "22dc22f8cedc58fcb11afe1acb08e9999e78be9c",
         "type": "github"
       },
       "original": {

nix/vagrant.nix

@@ -21,6 +21,7 @@
 , pkg-config
 , protobufPin
 , protoc-gen-doc
+, protoc-gen-go-grpc
 , ruby
 , zlib
 }:
@@ -41,6 +42,7 @@ mkShell rec {
 
     # Custom packages, added to overlay
     protobufPin
+    protoc-gen-go-grpc
     go-protobuf
     go-protobuf-json
     go-tools