python2.pkgs.wcwidth: add missing python2 dependency

pkgs/development/python2-modules/wcwidth/default.nix

···
+{ backports-functools-lru-cache
+, wcwidth
+}:
+
+wcwidth.overridePythonAttrs(oldAttrs: {
+  propagatedBuildInputs = oldAttrs.propagatedBuildInputs ++ [
+    backports-functools-lru-cache
+  ];
+})
+

pkgs/top-level/python2-packages.nix

···
     doCheck = false;  # circular dependency with pytest
   });
 
+  wcwidth = callPackage ../development/python2-modules/wcwidth {
+    inherit wcwidth;
+  };
+
   wheel = callPackage ../development/python2-modules/wheel { };
 
   zeek = disabled super.zeek;