Workaround for warnings about the parent pom

There used to be lots of warnings like this when Maven starts:

[WARNING] Some problems were encountered while building the effective model for fi.jumi:jumi-api:jar:0.5-SNAPSHOT
[WARNING] 'parent.relativePath' of POM fi.jumi:parent:0.5-SNAPSHOT (C:\DEVEL\Jumi\jumi\parent\pom.xml) points at fi.jumi:project instead of org.sonatype.oss:oss-parent, please verify your project structure @ fi.jumi:parent:0.5-SNAPSHOT, C:\DEVEL\Jumi\jumi\parent\pom.xml, line 6, column 13