Fix warning on playerid_lookup()
Fix warning on playerid_lookup()

Upon a call to playerid_lookup(), a DTypeWarning would appear stating
that Columns (8,9,10) had mixed types when reading the CSV file from
the Chadwick Register. Specified the types on those columns to suppress
the warning as well as lower memory footprint when reading the CSV
file.

Resolves: https://github.com/jldbc/pybaseball/issues/10

jldbc/pybaseball