use tycho version 0.20.0 for Eclise Luna compatibility

Tycho version 0.16.0 is not compatible with Maven 3.2, which is the
built in version in m2e for Eclipse Luna.
For the source-feature-plugin, we still use v0.16.0, since build of the
sdk feature fails with newer version ([ERROR] Missing sources for
plugins ...).    

Change-Id: I0b4078de6084e9bb93b87fc9a2bea3feb97f66be
Signed-off-by: Carsten Hiesserich <carsten.hie@gmail.com>
2 files changed