LSP: sourcegraph/go-langserver doesn't work

Dependencies:

export GOPATH=/home/user/go # the default location
go get -u github.com/sourcegraph/go-langserver
go get -u github.com/mdempsky/gocode

Go version: 1.10

Language client setings:

Name: Go
MIME: text/x-go
Executable: /home/user/go/bin/go-langserver
Arguments: -gocodecompletion

Then edit any Go file whatsoever, completion doesn't work, error messages appear, originating in https://github.com/sourcegraph/go-langserver/blob/master/langserver/ast.go#L26

I'm not entirely sure whom to blame here since it's weird that it wouldn't work at all like this.