README: drop python3.4 support

Python3.4 is no longer maintained (PEP 429 says March 2019 was the EOL date),
and the current version of pip (19.1) is the last to support it, so it's time
to let go.

* remove py34 from .travis.yml so PRs don't fail spuriously (there's some
  problem with txtorcon and twisted that only happens on py3.4)

.travis.yml

@@ -17,8 +17,6 @@ matrix:
   include:
     - python: 2.7
       script: tox -e py27-nodilate
-    - python: 3.4
-      script: tox -e py34-nodilate
     - python: 3.5
       script: tox -e py35-coverage
     - python: 3.6

README.md

@@ -28,5 +28,4 @@ or the docs/ subdirectory.
 
 This library is released under the MIT license, see LICENSE for details.
 
-This library is compatible with python2.7, 3.4 (non-Windows-only), 3.5,
-3.6, and 3.7.
+This library is compatible with python2.7, 3.5, 3.6, and 3.7.