message: fix 'superset db history'
  * fix 'superset db history'
  Related Error msg when running `superset db history`:
  "NameError: Can't invoke function 'get_bind', as the proxy object has not
  yet been established for the Alembic 'Operations' class.  Try placing
  this code inside a callable."
  * Lint
diff: @@ -34,11 +34,10 @@ datasources = sa.Table(
  sa.Column('datasource_name', sa.String(255)),
  )
  -bind = op.get_bind()
  -insp = sa.engine.reflection.Inspector.from_engine(bind)
  -
  def upgrade():
  + bind = op.get_bind()
  + insp = sa.engine.reflection.Inspector.from_engine(bind)
  # Add the new less restrictive uniqueness constraint.
  with op.batch_alter_table('datasources', naming_convention=conv) as batch_op:
  @@ -114,6 +113,8 @@ def upgrade():
  def downgrade():
  + bind = op.get_bind()
  + insp = sa.engine.reflection.Inspector.from_engine(bind)
  # Add the new more restrictive uniqueness constraint which is required by
  # the foreign key constraints. Note this operation will fail if the
  