Auto merge of #525 - Susurrus:min_rust, r=fiveop
Auto merge of #525 - Susurrus:min_rust, r=fiveop

Update minimum rust version to 1.9.0

This is largely because of features used in `tempfile` from 1.8 and 1.9. This was tested locally, so we'll see what CI says.

This does bring up the issue of the CI testing in the `ci` folder. That specifies the rust version as 1.7.0, but then when I looked at the docker images they seemed to only support 1.10, so maybe someone can comment on whether anything should be done about those things.

xd009642/nix,MarkusJais/nix-rust,berkowski/nix,Susurrus/nix,carllerche/nix-rust,Susurrus/nix,nix-rust/nix,xd009642/nix,kamalmarhubi/nix-rust,asomers/nix,geofft/nix-rust,asomers/nix,berkowski/nix,geofft/nix-rust,xd009642/nix,geofft/nix-rust,carllerche/nix-rust,kamalmarhubi/nix-rust,MarkusJais/nix-rust,kamalmarhubi/nix-rust,berkowski/nix,MarkusJais/nix-rust,nix-rust/nix,Susurrus/nix,carllerche/nix-rust