Replace tabs with spaces

Jekyll keeps complaining with 1.14 with errors like:
```
Regenerating: 2 files at 2014-08-12 16:27:15 Error reading file /home/michel/projects/rethinkdb-all/rethinkdb-www/docs/api/javascript/transformations/slice.md: (<unknown>): found a tab character that violate intendation while scanning a plain scalar at line 11 column 11
```


There were two tabs in the yaml format, I just replaced them with spaces.

@chipotle -- can you take a look at this?