[release-1.6] Update cel-cpp to fix CEL seg fault#217

Merged

istio-testing merged 2 commits intoistio:release-1.6from

May 18, 2020

Commits on May 15, 2020

Upgrade to cel-cpp v0.2.0 to pick up ANTLR thread-safety changes. (#514)

TristonianJones
authored and
mandarjog
committed
emit error if an error value is returned (#511)
mandarjog
committed