treewide: Escape backslash in strings properly

"\." is apparently the same as "." wheras the correct one is "\\."

nixos/modules/services/misc/geoip-updater.nix

···
 
     assertions = [
       { assertion = (builtins.filter
-          (x: builtins.match ".*\.(gz|xz)$" x == null) cfg.databases) == [];
+          (x: builtins.match ".*\\.(gz|xz)$" x == null) cfg.databases) == [];
         message = ''
           services.geoip-updater.databases supports only .gz and .xz databases.
 
···
           ${toString cfg.databases}
 
           Offending element(s):
-          ${toString (builtins.filter (x: builtins.match ".*\.(gz|xz)$" x == null) cfg.databases)};
+          ${toString (builtins.filter (x: builtins.match ".*\\.(gz|xz)$" x == null) cfg.databases)};
         '';
       }
     ];

pkgs/development/idris-modules/default.nix

···
     };
 
     files = builtins.filter (n: n != "default") (pkgs.lib.mapAttrsToList (name: type: let
-      m = builtins.match "(.*)\.nix" name;
+      m = builtins.match "(.*)\\.nix" name;
     in if m == null then "default" else builtins.head m) (builtins.readDir ./.));
   in (builtins.listToAttrs (map (name: {
     inherit name;

pkgs/top-level/impure.nix

···
           # it's a directory, so the set of overlays from the directory, ordered lexicographically
           let content = readDir path; in
           map (n: import (path + ("/" + n)))
-            (builtins.filter (n: builtins.match ".*\.nix" n != null || pathExists (path + ("/" + n + "/default.nix")))
+            (builtins.filter (n: builtins.match ".*\\.nix" n != null || pathExists (path + ("/" + n + "/default.nix")))
               (attrNames content))
         else 
           # it's a file, so the result is the contents of the file itself