bump version to 17.10

This will be the Hummingbird release

.version

···
-17.03
+17.10

nixos/modules/misc/version.nix

···
       nixosVersionSuffix = mkIf (pathIsDirectory gitRepo) (mkDefault (".git." + gitCommitId));
 
       # Note: code names must only increase in alphabetical order.
-      nixosCodeName = "Gorilla";
+      nixosCodeName = "Hummingbird";
     };
 
     # Generate /etc/os-release.  See