Update version to 1.2.0a1 (#584)

## Description

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Updates the version so we can tag a prerelease of 1.2.0

## Related Issue(s)

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<!-- i.e. "closes #0000" -->

## Breaking Change?

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## Checklist

- [ ] I have made corresponding changes to the documentation (if
required)
- [ ] I have added tests that prove my fix is effective or that my
feature works

cosmos/__init__.py

@@ -5,7 +5,7 @@
 
 Contains dags, task groups, and operators.
 """
-__version__ = "1.1.3"
+__version__ = "1.2.0a1"
 
 from cosmos.airflow.dag import DbtDag
 from cosmos.airflow.task_group import DbtTaskGroup