Fix utf8 errors

Fix #681

gns3server/controller/project.py

@@ -648,7 +648,7 @@ class Project:
             topo = project_to_topology(self)
             path = self._topology_file()
             log.debug("Write %s", path)
-            with open(path + ".tmp", "w+") as f:
+            with open(path + ".tmp", "w+", encoding="utf-8") as f:
                 json.dump(topo, f, indent=4, sort_keys=True)
             shutil.move(path + ".tmp", path)
         except OSError as e: