Update to mautrix-python 0.8.0.beta3

* Cross-server double puppeting is now possible
* End-to-bridge encryption no longer requires login_shared_secret,
  but the homeserver must support MSC2778 (Synapse 1.21+)

alembic/versions/888275d58e57_add_double_puppet_base_url_to_puppet_.py

@@ -0,0 +1,30 @@
+"""Add double puppet base URL to puppet table
+
+Revision ID: 888275d58e57
+Revises: a328bf4f0932
+Create Date: 2020-10-14 18:52:00.730666
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = '888275d58e57'
+down_revision = 'a328bf4f0932'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('puppet', schema=None) as batch_op:
+        batch_op.add_column(sa.Column('base_url', sa.Text(), nullable=True))
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('puppet', schema=None) as batch_op:
+        batch_op.drop_column('base_url')
+    # ### end Alembic commands ###