I am trying to use `mongodb: 0.9.1` crate in an `actix-web: 2.0` web server, I am having version conflict issue on `trust-dns-proto` dependency. Here is the output of `cargo build`: 

```

error: failed to select a version for `trust-dns-proto`.
... required by package `actix-connect v1.0.1`
... which is depended on by `actix-http v1.0.1`
... which is depended on by `actix-web v2.0.0`
... which is depended on by `stock-api v0.1.0 (/Users/sefa.balik/projects/keci/stock-api)`
versions that meet the requirements `= 0.18.0-alpha.2` are: 0.18.0-alpha.2

all possible versions conflict with previously selected packages.

previously selected package `trust-dns-proto v0.18.0`
... which is depended on by `mongodb v0.9.1`
... which is depended on by `stock-api v0.1.0 (/Users/sefa.balik/projects/keci/stock-api)`

failed to select a version for `trust-dns-proto` which could resolve this conflict

```