docs: Fix PATH environment variable formatting in developing.md

Author: tony

docs/developing.md

@@ -106,7 +106,7 @@ $ tmuxp
 [pytest] is used for tests.
 
 As you seen above, the `tmuxp` command will now be available to you,
-since you are in the virtual environment, your {}`PATH` environment was
+since you are in the virtual environment, your `PATH` environment was
 updated to include a special version of `python` inside your `.venv`
 folder with its own packages.