Add flake8-future-import to tox.ini

tox.ini

@@ -34,6 +34,8 @@ max-line-length = 79
 max-doc-length = 79
 verbose = 2
 statistics = True
+min-version = 2.7
+require-code = True
 exclude =
     .github/
     .tox/
@@ -65,6 +67,20 @@ ignore =
 ;    D402 First line should not be the function's "signature"
     D100, D101, D102, D103, D104, D105, D107
 
+;   -- flake8-future-import --
+;    x = 1 for missing, 5 for present
+;    FIx6 nested_scopes     2.2
+;    FIx7 generators        2.3
+;    FIx2 with_statement    2.6
+;    FIx1 absolute_import   3.0
+;    FIx0 division          3.0
+;    FIx3 print_function    3.0
+;    FIx4 unicode_literals  3.0
+;    FIx5 generator_stop    3.7
+;    ???? annotations       4.0
+;    FI90 __future__ import does not exist
+    FI50, FI51, FI53, FI54
+
 per-file-ignores =
 ;    F401 imported but unused
 ;    E402 module level import not at top of file
@@ -83,6 +99,7 @@ deps =
     flake8-commas
     flake8-comprehensions
     flake8-docstrings
+    flake8-future-import
     flake8-quotes
 skip_install = true
 commands =