Update minimum supported Rust version to 1.9.0
Update minimum supported Rust version to 1.9.0

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