Unable to use dict pragmas with sqliteq
Hi

https://github.com/coleifer/peewee/blob/master/playhouse/sqliteq.py#L228

Here for pragmas being dictionary it fails with 
```
...
    pdict = dict((k.lower(), v) for (k, v) in pragmas)
ValueError: too many values to unpack (expected 2)
```

Not sure how to better fix it in code. Not urgent also, I will just use list of tuples for now.