Upgrade database.

def upgrade():
    """Upgrade database."""
    def json_column(name, **kwargs):
        """Return JSON column."""
        return sa.Column(
            name,
            sqlalchemy_utils.types.JSONType().with_variant(
                postgresql.JSON(none_as_null=True), 'postgresql',
            ),
            **kwargs
        )

    op.create_table(
        'webhooks_events',
        sa.Column('created', sa.DateTime(), nullable=False),
        sa.Column('updated', sa.DateTime(), nullable=False),
        sa.Column(
            'id', sqlalchemy_utils.types.uuid.UUIDType(), nullable=False),
        sa.Column('receiver_id', sa.String(length=255), nullable=False),
        sa.Column('user_id', sa.Integer(), nullable=True),
        json_column('payload', nullable=True),
        json_column('payload_headers', nullable=True),
        json_column('response', nullable=True),
        json_column('response_headers', nullable=True),
        sa.Column('response_code', sa.Integer(), nullable=True),
        sa.ForeignKeyConstraint(['user_id'], [u'accounts_user.id'], ),
        sa.PrimaryKeyConstraint('id')
    )
    op.create_index(
        op.f('ix_webhooks_events_receiver_id'),
        'webhooks_events',
        ['receiver_id'],
        unique=False
    )