README.md: s/18.03/18.09/

README.md

@@ -119,7 +119,7 @@ If you have the `nix` package manager installed, you can create an IHaskell
 notebook environment with one command. For example:
 
 ```bash
-$ nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.03.tar.gz release-8.2.nix --arg packages "haskellPackages: [ haskellPackages.lens ]"
+$ nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.09.tar.gz release-8.2.nix --arg packages "haskellPackages: [ haskellPackages.lens ]"
 <result path>
 $ <result path>/bin/ihaskell-notebook
 ```
@@ -129,7 +129,7 @@ It might take a while the first time, but subsequent builds will be much faster.
 The IHaskell display modules are not loaded by default and have to be specified as additional packages:
 
 ```bash
-$ nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.03.tar.gz release-8.2.nix --arg packages "haskellPackages: [ haskellPackages.ihaskell-blaze haskellPackages.ihaskell-charts ]"
+$ nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.09.tar.gz release-8.2.nix --arg packages "haskellPackages: [ haskellPackages.ihaskell-blaze haskellPackages.ihaskell-charts ]"
 ```
 
 # Troubleshooting