Nix: bump to 2017-03-21

Partial cherry-pick, dropped hydra bump.

(cherry picked from commit 99632d5)

pkgs/tools/package-management/nix/default.nix

@@ -1,5 +1,5 @@
 { lib, stdenv, fetchurl, fetchFromGitHub, perl, curl, bzip2, sqlite, openssl ? null, xz
-, pkgconfig, boehmgc, perlPackages, libsodium, aws-sdk-cpp
+, pkgconfig, boehmgc, perlPackages, libsodium, aws-sdk-cpp, brotli
 , autoreconfHook, autoconf-archive, bison, flex, libxml2, libxslt, docbook5, docbook5_xsl
 , storeDir ? "/nix/store"
 , stateDir ? "/nix/var"
@@ -21,6 +21,7 @@ let
 
     buildInputs = [ curl openssl sqlite xz ]
       ++ lib.optional (stdenv.isLinux || stdenv.isDarwin) libsodium
+      ++ lib.optional fromGit brotli # Since 1.12
       ++ lib.optional (stdenv.isLinux && lib.versionAtLeast version "1.12pre")
           (aws-sdk-cpp.override {
             apis = ["s3"];
@@ -112,12 +113,12 @@ in rec {
 
   nixUnstable = lib.lowPrio (common rec {
     name = "nix-1.12${suffix}";
-    suffix = "pre5073_1cf4801";
+    suffix = "pre5110_165786d";
     src = fetchFromGitHub {
       owner = "NixOS";
       repo = "nix";
-      rev = "1cf480110879ffc8aee94b4b75999da405b71d7c";
-      sha256 = "1iwpddz0yni7cz2g9asj6nmrwhaai3rhfmkq954hph8nx02c3l02";
+      rev = "165786dbc0ca0b93fadb6e491defac603475b601";
+      sha256 = "0ah68ss5wlpgfpc4k7yl2h3szbwgllyn5d6s464vynaig6b165pz";
     };
     fromGit = true;
   });