[retrieve-and-rank] Using 1.7 packages for dealing with Files

[germanattanasio]

After running http://www.mojohaus.org/animal-sniffer/animal-sniffer-maven-plugin/examples/generating-java-signatures.html

util/ZipUtils.java:57: Undefined reference: String java.nio.file.Path.toString()
util/ZipUtils.java:61: Undefined reference: java.nio.file.Path java.nio.file.Files.walkFileTree(java.nio.file.Path, java.nio.file.FileVisitor)
util/ZipUtils.java:87: Undefined reference: String java.nio.file.Path.toString()
util/ZipUtils.java:64: Undefined reference: java.nio.file.FileVisitResult java.nio.file.FileVisitResult.CONTINUE
util/ZipUtils.java:69: Undefined reference: java.nio.file.FileVisitResult java.nio.file.FileVisitResult.CONTINUE
util/ZipUtils.java:74: Undefined reference: java.nio.file.Path java.nio.file.Path.relativize(java.nio.file.Path)
util/ZipUtils.java:74: Undefined reference: String java.nio.file.Path.toString()
util/ZipUtils.java:74: Undefined reference: byte[] java.nio.file.Files.readAllBytes(java.nio.file.Path)
util/ZipUtils.java:75: Undefined reference: java.nio.file.FileVisitResult java.nio.file.FileVisitResult.CONTINUE
util/ZipUtils.java:80: Undefined reference: java.nio.file.Path java.nio.file.Path.toAbsolutePath()
util/ZipUtils.java:81: Undefined reference: java.nio.file.Path java.nio.file.Path.getFileName()
util/ZipUtils.java:61: Undefined reference: java.nio.file.Path
util/ZipUtils.java:61: Undefined reference: java.nio.file.Path
util/ZipUtils.java:61: Undefined reference: java.nio.file.Path
util/ZipUtils.java:61: Undefined reference: java.nio.file.Path
RetrieveAndRank.java:360: Undefined reference: java.nio.file.Path java.io.File.toPath()
RetrieveAndRank.java:366: Undefined reference: java.nio.file.Path java.io.File.toPath()
RetrieveAndRank.java:366: Undefined reference: void java.nio.file.Files.delete(java.nio.file.Path)
RetrieveAndRank.java:366: Undefined reference: java.nio.file.Path java.io.File.toPath()
RetrieveAndRank.java:366: Undefined reference: void java.nio.file.Files.delete(java.nio.file.Path)

[germanattanasio]

To validate that the library is 1.6 compatible please add

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>animal-sniffer-maven-plugin</artifactId>
    <version>1.11</version>
    <executions>
        <execution>
            <phase>test</phase>
            <goals>
                <goal>check</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <signature>
            <groupId>org.codehaus.mojo.signature</groupId>
            <artifactId>java16</artifactId>
            <version>1.1</version>
        </signature>
    </configuration>
</plugin>

to the pom.xml