treewide: ReadWriteDirectories -> ReadWritePaths.

These were renamed in systemd v231:
https://github.com/systemd/systemd/commit/2a624c36e646e9ef8d204a506b12e7dbd380e111

nixos/modules/services/misc/zoneminder.nix

@@ -350,7 +350,7 @@ in {
           RestartSec = "10s";
           CacheDirectory = dirs cacheDirs;
           RuntimeDirectory = dirName;
-          ReadWriteDirectories = lib.mkIf useCustomDir [ cfg.storageDir ];
+          ReadWritePaths = lib.mkIf useCustomDir [ cfg.storageDir ];
           StateDirectory = dirs (lib.optionals (!useCustomDir) libDirs);
           LogsDirectory = dirName;
           PrivateTmp = true;

nixos/modules/services/security/step-ca.nix

@@ -107,7 +107,7 @@ in
           UMask = "0077";
           Environment = "HOME=%S/step-ca";
           WorkingDirectory = ""; # override upstream
-          ReadWriteDirectories = ""; # override upstream
+          ReadWritePaths = ""; # override upstream
 
           # LocalCredential handles file permission problems arising from the use of DynamicUser.
           LoadCredential = "intermediate_password:${cfg.intermediatePasswordFile}";

nixos/modules/services/web-servers/caddy/default.nix

@@ -368,7 +368,7 @@ in
         ExecReload = [ "" ''${cfg.package}/bin/caddy reload ${runOptions} --force'' ];
         User = cfg.user;
         Group = cfg.group;
-        ReadWriteDirectories = cfg.dataDir;
+        ReadWritePaths = [ cfg.dataDir ];
         StateDirectory = mkIf (cfg.dataDir == "/var/lib/caddy") [ "caddy" ];
         LogsDirectory = mkIf (cfg.logDir == "/var/log/caddy") [ "caddy" ];
         Restart = "on-failure";

nixos/modules/services/web-servers/traefik.nix

@@ -170,7 +170,7 @@ in {
         PrivateDevices = true;
         ProtectHome = true;
         ProtectSystem = "full";
-        ReadWriteDirectories = cfg.dataDir;
+        ReadWritePaths = [ cfg.dataDir ];
         RuntimeDirectory = "traefik";
       };
     };