How to add dependency to the boot class path?

Question

I'm trying to add the alpn-boot dependency to the boot class path. The following should work in the pom.xml file:

<properties>
    <jetty.alpn.path>${settings.localRepository}/org/mortbay/jetty/alpn/alpn-boot/${jetty.alpn.version}/alpn-boot-${jetty.alpn.version}.jar</jetty.alpn.path>
    <argLine.bootcp>-Xbootclasspath/p:${jetty.alpn.path}</argLine.bootcp>
    <jetty.alpn.version>8.1.6.v20151105</jetty.alpn.version>
</properties>

<plugin>
    <artifactId>maven-dependency-plugin</artifactId>
    <executions>
        <execution>
            <id>get-alpn-boot</id>
            <phase>validate</phase>
            <goals>
                <goal>get</goal>
            </goals>
            <configuration>
                <groupId>org.mortbay.jetty.alpn</groupId>
                <artifactId>alpn-boot</artifactId>
                <version>${jetty.alpn.version}</version>
            </configuration>
        </execution>
    </executions>
</plugin>

However, it definitely isn't being added to the boot class path. I'm running my application on Pivotal Web Services. Could it be to do with that? Or is there something wrong with my pom.xml file?