class definitions that don't inherit from another class don't need parentheses

[jspaaks]

grep -inrE "class .*\(\):"  ./asreview/**/*.py
./asreview/data/base.py:88:class ASReviewData():
./asreview/io/csv_reader.py:20:class CSVReader():
./asreview/io/csv_writer.py:15:class CSVWriter():
./asreview/io/excel_reader.py:21:class ExcelReader():
./asreview/io/excel_writer.py:15:class ExcelWriter():
./asreview/io/paper_record.py:116:class PaperRecord():
./asreview/io/ris_writer.py:19:class RISWriter():
./asreview/io/tsv_writer.py:15:class TSVWriter():
./asreview/webapp/sqlock.py:41:class SQLiteLock():

[jspaaks]

Also, classes don't need to inherit from object anymore. https://stackoverflow.com/a/45062077

[J535D165]

Resolved in #1404