http://nixos.org -> https://nixos.org

(cherry picked from commit 78bb17dd22e4da4e3810fbc78185d73bb25ea73e)
Signed-off-by: Domen Kožar <domen@dev.si>

nixos/doc/manual/development/sources.xml

@@ -50,8 +50,8 @@ Or, to base your local branch on the latest version available in the
 NixOS channel:
 
 <screen>
-$ curl -sI http://nixos.org/channels/nixos-unstable/ | grep Location
-Location: http://releases.nixos.org/nixos/unstable/nixos-14.10pre43986.acaf4a6/
+$ curl -sI https://nixos.org/channels/nixos-unstable/ | grep Location
+Location: https://releases.nixos.org/nixos/unstable/nixos-14.10pre43986.acaf4a6/
 
 $ git checkout -b local acaf4a6
 </screen>
@@ -92,4 +92,4 @@ to <command>nix-env</command>, as it will break after interpreting expressions
 in <filename>nixos/</filename> as packages.</para>
 -->
 
-</chapter>
+</chapter>