Use M2E p2 repo on eclipse.org instead of takari.io

Due to https://bugs.eclipse.org/bugs/show_bug.cgi?id=433653, it's better to build m2eclipse-tycho against http://download.eclipse.org/technology/m2e/milestones/1.5/ p2 repo on eclipse.org than the http://repository.takari.io:8081/nexus/content/sites/m2e.extras/m2e/1.5.0/N/LATEST/ (which is currently down) ?