confusing error message when overlay/match expects is not quoted

```yaml
---
id: 1
type: book
modified: false
---
id: 2
type: book
modified: false
---
id: 3
type: course
modified: false
```

```yaml
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all, expects=1+
---
modified: true
```

Gives you the error message
```yaml
- got ')', want primary expression
match-subset-docs.yml:2 | #@overlay/match by=overlay.all, expects=1+
```

What's confusing is that there isn't a `)` in the annotation that I wrote.

I was hoping it would print an error saying my `expects` input should be quoted. Or ideally it accepts the `1+` as a valid token (ie. without the quoting)

Start by reproducing the YAML and overlay annotation from the issue, then trace how the annotation parser handles the unquoted `expects=1+` value. Done means either accepting `1+` as a valid token or replacing the misleading `got ')', want primary expression` message with an error that explains the quoting requirement.

Written by the indexing model from the issue text.