Fix flaky phpcs-security-audit unit tests

Summary

The unit tests for the phpcs-security-audit project have been failing intermittently for at least the past 9 months:

• Jan 7, 2020
• Dec 2, 2019
• Apr 9, 2019

Improvements

Update convert_test.go so the order of the vulnerabilities doesn't impact the test.

Involved components

• convert_test.go