Wrong let expression parsing

The contents of `do` in the following code should be parsed as a sequence of let expression and x, but it's parsed as let expression in sequence of the sum and x.

```fsharp
do
let x = 1 in x + 1
x
```

In addition to the unexpected tree form it also creates a wrong scope for `x`.

[AST viewer](https://jindraivanek.gitlab.io/ast-viewer/#?code=CYewUABFEDYKYBcIA8IF4IEYIEsB2KEA1FpNMkA&defines=Q&filename=Q)