Fix gRPC capitalization

doc/administration/gitaly/index.md

@@ -885,7 +885,7 @@ you are seeing Gitaly errors. You can control the log level of the
 gRPC client with the `GRPC_LOG_LEVEL` environment variable. The
 default level is `WARN`.
 
-You can run a GRPC trace with:
+You can run a gRPC trace with:
 
 ```shell
 GRPC_TRACE=all GRPC_VERBOSITY=DEBUG sudo gitlab-rake gitlab:gitaly:check