Fix to add image name to issue body

[yokawasa]

Pull partial update made in wochinge/gitrivy to this forked repository

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In some case, trivy output doesn't include image name, thus, add image name as header to issueContent when vulnerabilities are detected

Here is the case where image name isn't included in issueContent image: my-image:latest (contain os image + jar )

trivy image --ignore-unfixed --severity HIGH,CRITICAL my-image:latest

my-image:latest (alpine 3.10.9)
==================================
Total: 0 (HIGH: 0, CRITICAL: 0)

my-app.jar
================
Total: 1 (HIGH: 1, CRITICAL: 0)
...