Updates jsilver to generate java8 bytecode.

Test: m jsilver. javap -p -v -cp out/host/linux-x86/framework/jsilver.jar  com/google/clearsilver/jsilver/values/StringValue | grep "major version" (outputs 52 instead of 53 now).

Bug: 170392930
Change-Id: Ia8e40364e7b6f8c2127c85009da71d3b91efb461