TypeError bug with calendar_helpers NP_NAT

[mdsalnikov]

trading_calendars/trading_calendars/calendar_helpers.py

Line 6 in 19c4b67

NP_NAT = np.array([pd.NaT], dtype=np.int64)[0]

This definition leads to TypeError: int() argument must be a string, a bytes-like object or a number, not 'NaTType'

[maread99]

@MihailSalnikov this package isn't being maintained (see the README) although a fork exchange_calendars is being maintained and this issue was resolved in the latest release (3.2).