Fix license attribute of many bsd-like licensed packages

pkgs/applications/window-managers/bspwm/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation rec {
     description = "A tiling window manager based on binary space partitioning";
     homepage = http://github.com/baskerville/bspwm;
     maintainers = [ stdenv.lib.maintainers.meisternu ];
-    license = "BSD";
+    license = stdenv.lib.licenses.bsd2;
     platforms = stdenv.lib.platforms.linux;
   };
 }

pkgs/applications/window-managers/herbstluftwm/default.nix

@@ -19,7 +19,7 @@ stdenv.mkDerivation rec {
   meta = {
     description = "A manual tiling window manager for X";
     homepage = "http://herbstluftwm.org/";
-    license = "BSD"; # Simplified BSD License
+    license = stdenv.lib.licenses.bsd2;
     platforms = stdenv.lib.platforms.linux;
   };
 }

pkgs/applications/window-managers/sxhkd/default.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
   meta = {
     description = "Simple X hotkey daemon";
     homepage = "http://github.com/baskerville/sxhkd";
-    license = "BSD";
+    license = stdenv.lib.licenses.bsd2;
     platforms = stdenv.lib.platforms.linux;
   };
 }