Update db.py

[Tortar]

this should fix issue #3 (comment)

[minamotorin]

When I opened #3, I seem to have misunderstood config.Database="filename" as twint.run.db, sorry.
I don't know what was the problem with db.py, but I will merge this PR if I understand it.

@Tortar
Can you show me an example code for the problem resolved in this PR?

[Tortar]

Yes, here it is:

Writing in terminal twint -s a -db a.db gives

File "\.", line 293, in tweets
    cursor.execute(query, (Tweet.id, int(reply['user_id']), reply['username']))
KeyError: 'user_id'

after fixing it, the program will throw exceptions on the other two lines of code because Tweet.mentions is a list of dicts and so the join method can't be used on it without first converting the dicts in strings, while Tweet.place is a dict and so can't be inserted in the db if you don't convert it to string.

[minamotorin]

@Tortar
Thanks! I confirmed the behavior.
But I think it's better to put this PR on hold.
The reason is followings.

• twint.run.db doesn't work #3 was written with the intention of Incorrect values of stored objects #13 (my explanation was insufficient)
• The cause of twint.run.db doesn't work #3 is considered to be the same as the cause of Incorrect values of stored objects #13
• Then, fix for twint.run.db doesn't work #3 and fix for Incorrect values of stored objects #13 can conflict
• The fix for Incorrect values of stored objects #13 is more fundamental, so it should be prioritized

After fixing #13 completely, if this PR still useful, I'll merge this PR.

Any other opinions are welcome.

[minamotorin]

I merge this because I think #13 isn't fixed for a while.