Pin backports.os with correct Python version #120

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

requirements.txt

@@ -3,4 +3,4 @@ enum34==1.1.6 ; python_version < '3.4'
 pytz
 setuptools
 six==1.10.0
-backports.os
+backports.os=0.1.1

setup.py

@@ -38,7 +38,7 @@
  extras_require={
  "scandir :python_version < '3.5'": ['scandir~=1.5'],
  ":python_version < '3.4'": ['enum34~=1.1.6'],
- ":python_version < '3.0'": ['backports.os'],
+ ":python_version < '3.2'": ['backports.os~=0.1.1'],
  },
  entry_points={'fs.opener': [
  'ftp = fs.opener.ftpfs:FTPOpener',