Java 7 compile error

for 2.0 branch on java 7

mvn clean install -DskipTests

[ERROR] Failed to execute goal org.codehaus.mojo:animal-sniffer-maven-plugin:1.18:check (check-java-version) on project pdfbox-parent: Execution check-java-version of goal org.codehaus.mojo:animal-sniffer-maven-plugin:1.18:check failed: Unable to load the mojo 'check' in the plugin 'org.codehaus.mojo:animal-sniffer-maven-plugin:1.18' due to an API incompatibility: org.codehaus.plexus.component.repository.exception.ComponentLookupException: org/codehaus/mojo/animal_sniffer/maven/CheckSignatureMojo : Unsupported major.minor version 52.0