libcouchbase: 2.7.6 -> 2.8.4

Semi-automatic update. These checks were performed:

- built on NixOS
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc help` got 0 exit code
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc version` and found version 2.8.4
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc-pillowfight --help` got 0 exit code
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc-n1qlback --help` got 0 exit code
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc-n1qlback --help` and found version 2.8.4
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc-subdoc --help` got 0 exit code
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc-subdoc --help` and found version 2.8.4
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc-proxy --help` got 0 exit code
- ran `/nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4/bin/cbc-proxy --help` and found version 2.8.4
- found 2.8.4 with grep in /nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4
- found 2.8.4 in filename of file in /nix/store/ag3ka0qv88321ih0gdn743p167vqmvdn-libcouchbase-2.8.4