change version number to 1.2.0 for OBS Epoch release

[yimingwangdell]

Purpose

Resolves #980

change version number to 1.2.0

PR checklist

• [ ] Add link to the issue
• [ ] Choose Project
• [ ] Choose PR label
• [ ] New unit tests added
• [ ] Modified code has meaningful comments
• [ ] All TODOs are linked with the issues
• [ ] All comments are resolved

Testing

Provide test details

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (82879b1) 72.20% compared to head (4da4b77) 72.20%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #979 +/- ## ======================================= Coverage 72.20% 72.20% ======================================= Files 62 62 Lines 8044 8044 ======================================= Hits 5808 5808 Misses 1985 1985 Partials 251 251 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `72.20% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dell#carryforward-flags-in-the-pull-request-comment) to find out more. Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dell). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dell)

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