fix(redhat): detect RedHat version

[MaineK00n]

What did you implement:

In this part, we are trying to validate the major version, but release is supposed to be in the form of 8.5, which will cause an error in strings.Atoi(release).
This PR fixes the validation to the major version correctly.

vuls/scanner/redhatbase.go

Lines 151 to 158 in 671be3f

	ver, err := strconv.Atoi(release)
	if err != nil {
	logging.Log.Warnf("Failed to parse RedHat/CentOS version number: %s", release)
	return true, newCentOS(c)
	}
	if ver < 5 {
	logging.Log.Warnf("Versions prior to RedHat/CentOS 5 are not supported, detected version is %s", release)
	}

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

master

$ vuls configtest
vuls configtest
[Feb 11 20:16:31]  INFO [localhost] vuls-v0.19.3-build-20220211_201157_671be3f
[Feb 11 20:16:31]  INFO [localhost] Validating config...
[Feb 11 20:16:31]  INFO [localhost] Detecting Server/Container OS... 
[Feb 11 20:16:31]  INFO [localhost] Detecting OS of servers... 
[Feb 11 20:16:31]  WARN [localhost] Failed to parse RedHat/CentOS version number: 8.5
[Feb 11 20:16:31]  INFO [localhost] (1/1) Detected: vagrant:
...

MaineK00n/fix-detect-redhat-version

go run cmd/vuls/main.go configtest
[Feb 11 20:16:24]  INFO [localhost] vuls-`make build` or `make install` will show the version-
[Feb 11 20:16:24]  INFO [localhost] Validating config...
[Feb 11 20:16:24]  INFO [localhost] Detecting Server/Container OS... 
[Feb 11 20:16:24]  INFO [localhost] Detecting OS of servers... 
[Feb 11 20:16:24]  INFO [localhost] (1/1) Detected: vagrant: redhat 8.5
...

Checklist:

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• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
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Is this ready for review?: YES

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