YAML output issues

Similar to #306, using same commit of both api-linter and googleapis/googleapis.

Issues:

- Arrays elements printed for files with no problems.
- I think this invalid YAML but might be wrong - string values printed across multiple lines with various quoting, for example:

```yaml
- message: Use the `google.api.field_behavior` annotation instead of " Required.
CLDR region code of the country/region of the address. This" in the leading
comments. For example, `string name = 1 [(google.api.field_behavior) = REQUIRED];`.
```

Unrelated to YAML, but probably not worth filing another issue: `api-linter` exits with code 0 if there are lint issues. This may be by design though.

```
$ api-linter google/type/*.proto
- file_path: google/type/calendar_period.proto
problems: []
- file_path: google/type/color.proto
problems: []
- file_path: google/type/date.proto
problems: []
- file_path: google/type/dayofweek.proto
problems: []
- file_path: google/type/expr.proto
problems: []
- file_path: google/type/fraction.proto
problems: []
- file_path: google/type/latlng.proto
problems: []
- file_path: google/type/money.proto
problems:
- message: Fields representing timestamps should use `google.protobuf.Timestamp`.
location:
start_position:
line_number: 43
column_number: 3
end_position:
line_number: 43
column_number: 19
rule_id: core::0142::time-field-type
rule_doc_uri: https://googleapis.github.io/api-linter/rules/core/0142-time-field-type.html
- file_path: google/type/postal_address.proto
problems:
- message: Use the `google.api.field_behavior` annotation instead of " Required.
CLDR region code of the country/region of the address. This" in the leading
comments. For example, `string name = 1 [(google.api.field_behavior) = REQUIRED];`.
location:
start_position:
line_number: 52
column_number: 3
end_position:
line_number: 52
column_number: 26
rule_id: core::0203::required
rule_doc_uri: https://googleapis.github.io/api-linter/rules/core/0203-required.html
- file_path: google/type/quaternion.proto
problems: []
- file_path: google/type/timeofday.proto
problems:
- message: Fields representing timestamps should use `google.protobuf.Timestamp`.
location:
start_position:
line_number: 41
column_number: 3
end_position:
line_number: 41
column_number: 21
rule_id: core::0142::time-field-type
rule_doc_uri: https://googleapis.github.io/api-linter/rules/core/0142-time-field-type.html
- message: Fields representing timestamps should use `google.protobuf.Timestamp`.
location:
start_position:
line_number: 44
column_number: 3
end_position:
line_number: 44
column_number: 19
rule_id: core::0142::time-field-type
rule_doc_uri: https://googleapis.github.io/api-linter/rules/core/0142-time-field-type.html
```