Fix pipe operator ('|') precedence

https://github.com/pallets/jinja/issues/882

Current precedence of pipe operator doesn't follow the original jinja2 rules. Need to be fixed. This code:
```
2 < 6 | bool | string
```
should be interpreted as:
```
2 < (6 | bool | string)
```
instead of
```
(2 < 6) | bool | string
```

