Debian stretch is supported until Jun 2022.

MyRocks definitavely does require 1.1.3+.

Mroonga has never been zstd enabled, though
support for it exists in the codebase.

While a 1.1.3+ version exists in stretch backports
we don't support this.

Fixes: b67210b1054118fe14b6346bdee3f9bbd3416870