should alembic be listed as a dependency

[suliuzh]

General information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Windows 10
• ElasticHQ Version: latest
• Elasticsearch Version: latest
• Python version (ignore is using docker image): Python 3.6.5
• Browser Vendor and Version (if applicable):

Issue Description

Hi
I notice alembic is used in source code. But it seems alembic is not installed when "pip install elasticsearch-HQ". So I am wondering if alembic should be listed as a dependency.