[BUG] Boolean App filters raise error when used
Using the filter bar in the App to filter on a boolean field raises an error on `fiftyone==0.13.2`:

```py
import fiftyone as fo

sample = fo.Sample(filepath="/path/to/image.png", bool=True)

dataset = fo.Dataset()
dataset.add_sample(sample)

# Try selecting bool -> True in App
session = fo.launch_app(dataset)
```

```
Server Error

An exception has been raised by the server. Your session has been reverted to its previous state.

Traceback (most recent call last):
  File "main.py", line 271, in wrapper
    result = await func(self, *args, **kwargs)
  File "main.py", line 518, in on_message
    await event(self, **message)
  File "main.py", line 586, in on_filters_update
    await self.send_statistics(view, filters=filters, extended=True)
  File "main.py", line 1010, in send_statistics
    aggregations = fos.DatasetStatistics(view, filters).aggregations
  File "/Users/Brian/dev/env/tmp3/lib/python3.6/site-packages/fiftyone/core/state.py", line 167, in __init__
    self._aggregations = self._build(view, filters)
  File "/Users/Brian/dev/env/tmp3/lib/python3.6/site-packages/fiftyone/core/state.py", line 277, in _build
    else filters[field_name]["values"]
KeyError: 'values'
```

diff --git a/fiftyone/core/aggregations.py b/fiftyone/core/aggregations.py
index b0018fc49..a83bfacd1 100644
--- a/fiftyone/core/aggregations.py
+++ b/fiftyone/core/aggregations.py
@@ -508,7 +508,6 @@ class CountValues(Aggregation):
         Returns:
             a dict mapping values to counts
         """
-
         if self._first is None:
             return {i["k"]: i["count"] for i in d["result"]}
 
diff --git a/fiftyone/core/state.py b/fiftyone/core/state.py
index 73098feef..061138268 100644
--- a/fiftyone/core/state.py
+++ b/fiftyone/core/state.py
@@ -265,10 +265,9 @@ class DatasetStatistics(object):
                 aggregations.append(foa.Count(field_name))
                 if _meets_type(field, (fof.IntField, fof.FloatField)):
                     aggregations.append(foa.Bounds(field_name))
-                elif _meets_type(
-                    field,
-                    (fof.BooleanField, fof.StringField, fof.ObjectIdField),
-                ):
+                elif _meets_type(field, fof.BooleanField):
+                    aggregations.append(foa.CountValues(field_name, _first=3))
+                elif _meets_type(field, (fof.StringField, fof.ObjectIdField)):
                     include = (
                         None
                         if filters is None
['fiftyone/core/aggregations.py', 'fiftyone/core/state.py']