wrong line reported in 'did not find expected key while parsing a block mapping'

When parsing this yaml

```
key_one:
  inner:
  - value1
  - value2

key_two:
    inner:
  - value1
  - value2
```

the error message

```
Psych::SyntaxError: (/tmp/oops.yaml): did not find expected key while parsing a block mapping at line 1 column 1
```

contains the wrong line number. It should be reporting line 7 column 5.
