xmag: add libx11 as direct dep (fixes linkage)

Closes #861.

Signed-off-by: Maxim Belkin <maxim.belkin@gmail.com>

Author: maxim-belkin

Formula/x/xmag.rb

@@ -9,6 +9,7 @@ class Xmag < Formula
   depends_on "pkg-config" => :build
   depends_on "util-macros" => :build
   depends_on "xorgproto" => :build
+  depends_on "libx11"
   depends_on "libxaw"
   depends_on "libxmu"
   depends_on "libxt"