remove tests for python 2.7 and 3.4

The code is not compatible with 2.7
lxml used in the code requires >=3.5

Signed-off-by: Karol Gugala <kgugala@antmicro.com>

tox.ini

diff --git a/tox.ini b/tox.ini
index 4db88ab..23d3730 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,8 +5,6 @@
 setenv =
     PYTHONPATH={toxinidir}/v2x
 basepython =
-    py27: python2.7
-    py34: python3.4
     py35: python3.5
     py36: python3.6
     py37: python3.7
@@ -23,8 +21,6 @@
     # `setup.py check` is not needed. If your project contains a README.rst,
     # use `python setup.py check -m -r -s` instead.
     python setup.py check -m -s
-    # in sdfyacc.py we need to import sdflex.tokens, which are implicitly
-    # used by parser. This triggers flake8 error. Let's ignore this for now.
     flake8 .
 [flake8]
 exclude = .tox,*.egg,build,data