Update observability dependency libcircllhist

*Title*: *Update observability dependency `libcircllhist`*

*Description*:
When trying to update the observability dependencies in https://github.com/envoyproxy/envoy/pull/12799 the latest `libcircllhist` the following tests fail with not returning expected results.

- envoy/bazel-out/k8-fastbuild/testlogs/test/common/stats/thread_local_store_test/test.log
- envoy/bazel-out/k8-fastbuild/testlogs/test/extensions/stats_sinks/hystrix/hystrix_test/test.log
- envoy/bazel-out/k8-fastbuild/testlogs/test/server/admin/prometheus_stats_test/test.log
- envoy/bazel-out/k8-fastbuild/testlogs/test/server/admin/stats_handler_test/test.log

I lost the detailed logs with subsequent commits but will try to reproduce

*Relevant Links*:
The commits / changes between the lastest June 25 2020 commit and the current Envoy commit on February 11 2019 is https://github.com/circonus-labs/libcircllhist/compare/63a16dd6f2fc7bc841bb17ff92be8318df60e2e1...18f1b97603757d5e65baefa65b90d6ec182e8a30