Fix CucumberMissedExamplesInspection.

In the previous version of the inspection the following scenario outline does not trigger an error:

```
Scenario outline:
  Given step1
  Then step2
```

but this one does:

```
Scenario outline: scenario description
  Given step1
  Then step2
```

Triggering of the error must not be conditional to the presence of a description text since it is optional.

I decided to only  _highlight_ the "Scenario Outline:" part since code is simpler and it seems enough for the user to know that something is wrong. When present, we could also _highlight_ the description text but I don't see any obvious business value to this conditional.