nixos/samba: remove space in "[ global ]" heading

Use consistent no-space style. (All documentation I've seen use no
space, and the generated section headings from the NixOS module also use
no space.)

nixos/modules/services/network-filesystems/samba.nix

@@ -28,7 +28,7 @@ let
   configFile = pkgs.writeText "smb.conf"
     (if cfg.configText != null then cfg.configText else
     ''
-      [ global ]
+      [global]
       security = ${cfg.securityType}
       passwd program = /run/wrappers/bin/passwd %u
       pam password change = ${smbToString cfg.syncPasswordsByPam}