config: generate secret key using python

config.py.example

@@ -1,7 +1,8 @@
-import os
+import os, random, string
-import subprocess
+
 
 class Config:
-    SECRET_KEY = os.environ.get('SECRET_KEY') or subprocess.check_output(['pwgen', '20', '1'])
+    SECRET_KEY = os.environ.get('SECRET_KEY') or \
+            ''.join(random.choices(string.ascii_letters, k=20))
     DATA_DIR   = os.environ.get('DATA_DIR') or '/home/orange/devel/prolefeeder/tmp'
     MAX_LENGTH = os.environ.get('MAX_LENGTH') or 180