[circleci] allow codecov to fail
[circleci] allow codecov to fail

codecov failed in https://circleci.com/gh/3scale/apicast/9097

```
bash: line 1: html: No such file or directory
bash: line 2: syntax error near unexpected token `<'
```

3scale/docker-gateway,3scale/apicast,3scale/apicast,3scale/docker-gateway,3scale/apicast,3scale/apicast