ibis.postgres table expressions dont recognize inet datatype

[esamuel1]

xref #2461

Impacts ibis 1.3.0

Ibis doesn't appear to recognize inet data types in postgres when trying to build an ibis table expression. A simple reproduction of the issue is below:

pgcon = ibis.postgres.connect(
    database=database,
    host=host,
    user=user,
    password=password,
    port=port
)

tblnm='iptbl'
iptbl='''
create table if not exists {} (
sometime timestamp,aip inet);
'''.format(tblnm)
pgcon.raw_sql(iptbl)
iptblibis=pgcon.table(tblnm)

NotImplementedError: Could not find signature for dtype: <PGDialect_psycopg2, INET>
Looking at the sqlalchemy docs, it seems they do support inet for postgres.

[cpcloud]

Didn't get caught by GitHub in the merge.