`this_dir` in import statements fail when sample file in current directory

this_dir fails to expand properly for files in an import section if the importing sample file is contained in the current working directory, eg:

$ fast_curator_check control_regions_15_11_18/all_samples.yml 
Traceback (most recent call last):
  File "/users/bk17414/.local/bin/fast_curator_check", line 11, in <module>
    sys.exit(main_check())
  File "/users/bk17414/.local/lib/python2.7/site-packages/fast_curator/__main__.py", line 69, in main_check
    datasets += read.from_yaml(infile)
  File "/users/bk17414/.local/lib/python2.7/site-packages/fast_curator/read.py", line 37, in from_yaml
    datasets_dict = _load_yaml(path)
  File "/users/bk17414/.local/lib/python2.7/site-packages/fast_curator/read.py", line 29, in _load_yaml
    with open(path, 'r') as f:
IOError: [Errno 2] No such file or directory: 'control_regions_15_11_18/all_samples.yml'