Fix location data bug for string interpolations

An off-by-one error in tokenization caused bugs like seen in #3348:
```
*
[stdin]:1:1: error: unexpected *
*
^

"#{*}"
[stdin]:1:3: error: unexpected *
"#{*}"
  ^

"#{"#{*}"}"
[stdin]:1:5: error: unexpected *
"#{"#{*}"}"
    ^
```

This should fix, I think.