Use cwd when running haxelib path

If a local haxelib repo is being used, then moving out of the cwd will break library resolution.

This was presumably done in case `haxelib` is not in `PATH`, but in that situation `HAXEPATH` is unlikely to have been set either.

tools/hxcpp/PathManager.hx

@@ -106,7 +106,7 @@ class PathManager
 
          try
          {
-            output = ProcessManager.runProcess(Sys.getEnv ("HAXEPATH"), "haxelib", [ "path", name ], true, false);
+            output = ProcessManager.runProcess("", "haxelib", [ "path", name ], true, false);
          }
          catch (e:Dynamic) {}