fix: add spaces to the "command expected at line"'s

[xirzo]

"Command expected at line" do have spaces after them, while other errors do have those:

Source

if (!handled) {
  TokenPtr token = session->Current();
  std::string message = "Unknown top-level declaration: " + token->GetLexeme() + " at line " +
                        std::to_string(token->GetPosition().GetLine()) + " column " +
                        std::to_string(token->GetPosition().GetColumn());

  return std::unexpected(BytecodeParserError(message));
}

That results in text concatenation:

➜  TestOvum ovumc -m main.ovum -o main.oil && ovum-vm -f main.oil
Parser error: Command expected at line11

Fixed:

➜  TestOvum ovumc -m main.ovum -o main.oil && ovum-vm -f main.oil
Parser error: Command expected at line 11