Snyk CLI utilises the output from maven-dependency-plugin version 2.2
In versions 1 and 2 of Maven, the plugin version was lower than 2.2, and doesn't provide output in the required format, resulting in the Snyk error.
To use a higher version of the Maven Dependency Plugin, you can either upgrade Maven or specify which version you want to use in the build plugin management section of your project.
Version 2.2 of the maven-dependency-plugin needs some extra repository configuration because by default http is used. Maven Central now demands https to download. See https://blog.sonatype.com/central-repository-moving-to-https for more information.