Fix None access exception

[tyru]

When empty entry in config like this:

policies:

vint always raises an exception.

AttributeError: 'NoneType' object has no attribute 'keys'

[tyru]

CI failed but I don't know how to fix this...

[blueyed]

Thanks, remove support for Python 3.4, and rebased it.
Might be good to have a test, and/or better error message in this case.

[coveralls]

Coverage decreased (-0.1%) to 96.28% when pulling 7758955 on tyru:fix-none-empty-entry into 427de13 on Kuniwak:master.

[codecov-io]

Codecov Report

Merging #344 into master will decrease coverage by 0.14%.
The diff coverage is 68.18%.

@@           Coverage Diff            @@
##           master   #344      +/-   ##
========================================
- Coverage   94.14%    94%   -0.15%     
========================================
  Files         133    133              
  Lines        4152   4167      +15     
  Branches      417    418       +1     
========================================
+ Hits         3909   3917       +8     
- Misses        150    156       +6     
- Partials       93     94       +1

[tyru]

@blueyed sorry, I have no enough time to do it.
if you feel 7758955 is good, please merge it,
or wait until for a while... or you can implement it :)