Docs: bad text wrapping

On the page http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/analysis-synonym-tokenfilter.html

even on a huge monitor the text is being wrapped the next way
```
mapping:
ipod, i-pod, i pod => ipod, i-pod, i pod
mapping:
ipod, i-pod, i pod => ipod
```

So one can think that "mapping:" is not in comment and is a part of syntax. But the lines are less than 80 chars, so perhaps the problem is in the page layout and there may be some other pages in the reference where the text is also being wrapped in an undesirable way.

Closes #7739