Add missing argument in os.path.islink()

Hi,

The python script was throwing a `TypeError`, adding `__file__` as an argument fixed it for me.

```python
Traceback (most recent call last):
  File "/Users/corentin/project/perso/code_swarm/bin/code_swarm", line 249, in <module>
    main()
  File "/Users/corentin/project/perso/code_swarm/bin/code_swarm", line 76, in main
    proj_cfg = autogenerate_files(options)
  File "/Users/corentin/project/perso/code_swarm/bin/code_swarm", line 185, in autogenerate_files
    cp_tpl = os.path.join(root_path(), "bin", "config.template")
  File "/Users/corentin/project/perso/code_swarm/bin/code_swarm", line 100, in root_path
    if os.path.islink():
TypeError: islink() takes exactly 1 argument (0 given)
```