Use upper case for reference source for amino acid sequence

[zhuchcn]

Description

Sorry I missed this in the morning. I forgot that our amino acid sequence also has the function to infer reference source. It now also takes upper case values. So we should be good to go.

Closes #761

Checklist

• This PR does NOT contain PHI or germline genetic data. A repo may need to be deleted if such data is uploaded. Disclosing PHI is a major problem.
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• The name of the branch is meaningful and well formatted following the standards, using [AD_username (or 5 letters of AD if AD is too long)]-[brief_description_of_branch].
• I have added the major changes included in this pull request to the CHANGELOG.md under the next release version or unreleased, and updated the date.
• All test cases passed locally.

[lydiayliu]

Is this ready for review?