Upgrade scala to enable support for Oracle Java 8.

The version of scala referenced in build.gradle, 2.10.1 does not support
Oracle Java 8, resulting in compilation errors. Scala supports Java 8 from
version 2.10.3. Therefore, we change the version from 2.10.1 to 2.10.3.

Signed-off-by: Thorsten Fischer <thorsten@froschi.org>