rustc: 1.5.0 -> 1.6.0

pkgs/development/compilers/rustc/default.nix

···
 { stdenv, callPackage }:
 
 callPackage ./generic.nix {
-  shortVersion = "1.5.0";
+  shortVersion = "1.6.0";
   isRelease = true;
   forceBundledLLVM = false;
   configureFlags = [ "--release-channel=stable" ];
-  srcSha = "1vfpwx6a2f2rn528774cz9r7r82ppycn8z8ybll6bphdw7cyar1g";
+  srcSha = "1dvpiswl0apknizsz9bcrjnc4c43ys191a1b9gm3569xdlmxr36w";
 
   /* Rust is bootstrapped from an earlier built version. We need
   to fetch these earlier versions, which vary per platform.