cargo update -p flate2:1.0.1 --aggressive

This updates the `flate2` we use in production.  We also pull in
`flate2:0.2.20` via `conduit-git-http-backend` which is a middleware
that is only enabled in development.

This addresses four instances of "Conditional jump or move depends on
uninitialised value(s)" raised when running
`valgrind --trace-children=yes cargo test`

Author: jtgeibel