Do not use Semver for Apache Tomcat Importer

[TG1999]

./manage.py import vulnerabilities.importers.apache_tomcat.ApacheTomcatImporter Importing data using vulnerabilities.importers.apache_tomcat.ApacheTomcatImporter 'M5' is not a valid SemverVersion InvalidVersion("'M5' is not a valid <class 'univers.versions.SemverVersion'>") 'M1' is not a valid SemverVersion InvalidVersion("'M1' is not a valid <class 'univers.versions.SemverVersion'>") 'RC1' is not a valid SemverVersion InvalidVersion("'RC1' is not a valid <class 'univers.versions.SemverVersion'>") Successfully imported data using vulnerabilities.importers.apache_tomcat.ApacheTomcatImporter