Fix writing catalog csv files on Windows

[mherrmann3]

Problem: on Windows, csep.catalogs.AbstractBaseCatalog.write_ascii() interleaves every entry with an empty line, like so.:

lon,lat,mag,time_string,depth,catalog_id,event_id

-115.2228333,32.3463333,3.99,2005-01-02T20:58:48.280000,5.987,,ci10070917

-117.4448333,34.1238333,4.42,2005-01-06T14:35:27.680000,6.148,,ci14116972

Those files can also not be read by csep.load_catalog() (IndexError: list index out of range)

Solution: add newline='' to open(filename, write_string), see docs.python.org/3/library/csv (footnote) and stackoverflow.com/a/3348664

FYI: .write_json() is not affected, and there is no further occurrence in pyCSEP that needs to be fixed (b/c there is no further use of csv.DictWriter or csv.writer).

Type of change:

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have performed a self-review of my own code
• My changes generate no new warnings

[pabloitu]

related to #237. Todo: check PR in windows/linux and create unit-test for windows.

[pabloitu]

works ok for me!