Filtering not working for boolean data.

[kaiayoung]

This is probably a quick fix, but we may also want to create some custom filtering options in the operator menu for boolean data. Sample code:

import pandas as pd
import numpy as np
import json
import random
from ipydatagrid import DataGrid, TextRenderer, Expr
n = 5
df = pd.DataFrame({
    'Value 1': [random.choice([True, False]) for i in range(n)],
    'Value 2': [random.choice([True, False]) for i in range(n)],
    'Value 3': [random.choice([True, False]) for i in range(n)],
    'Value 4': [random.choice([True, False]) for i in range(n)],
})

jsontable = json.loads(df.to_json(orient='table'))
DataGrid(data=jsontable)

[martinRenou]

Fixed by #46