Does not work with NixOS

Since NixOS handles packages quite differently and does not depend on standard linux paths like /lib, /bin, etc - the downloaded binary does not execute. Exception:
```
Execution failed for task ':rpc:generateProto'.
> java.io.IOException: Cannot run program "/home/gytis/.local/share/gradle/caches/modules-2/files-2.1/com.google.protobuf/protoc/3.6.1/f8584d1e86d1adb61d9c559e4b49cedbc97c4d78/protoc-3.6.1-linux-x86_64.exe": error=2, No such file or directory
```

Temp workaround:
Install `protobuf` package manually and define this in your config:
```
protoc {
path = 'protoc'
}
```