nixos/tests/chromium: Propagate "system" to pkgs

Assigning the channelMap by the function attrset argument at the
top-level of the test expression file may reference a different
architecture than we need for the tests.

So if we get the pkgs attribute by auto-calling, this will lead to test
failure because we have a different architecture for the test than for
the browser.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

nixos/tests/chromium.nix

@@ -1,5 +1,5 @@
 { system ? builtins.currentSystem
-, pkgs ? import ../.. {}
+, pkgs ? import ../.. { inherit system; }
 , channelMap ? {
     stable = pkgs.chromium;
     beta   = pkgs.chromiumBeta;