Convert non-breaking space in yaml to normal space

**Is this a BUG REPORT or FEATURE REQUEST?**:
FEATURE REQUEST

**What happened?**:

If task yaml file has [non-breaking space](https://en.wikipedia.org/wiki/Non-breaking_space), it may cause some unexpected result. For example, if there is a non-breaking space at the beginning of the cmd step, the step will be skipped in the execution.

```
 - cmd
```

**What did you expect to happen?**:

Convert non-breaking space to normal space.

Here is an example https://github.com/travis-ci/travis-core/pull/227