Include Robolectric snapshot via Sonatype OSS repository.

Local install no longer needed. Simply add (and activate) the following profile in settings.xml.

```
<settings>
    ...
    <activeProfiles>
        <activeProfile>snapshots</activeProfile>
        ...
    </activeProfiles>
    <profiles>
        <profile>
            <id>snapshots</id>
            <repositories>
                <repository>
                    <id>snapshots-repo</id>
                    <url>https://oss.sonatype.org/content/repositories/snapshots/</url>
                    <releases>
                        <enabled>false</enabled>
                    </releases>
                    <snapshots>
                        <enabled>true</enabled>
                    </snapshots>
                </repository>
            </repositories>
        </profile>
        ...
    </profiles>
    ...
</settings>
```