[AIRFLOW-3426] Bugfix / Correct Python Version Documentation Reference (

apache#4259)

- Change all Python 3.4 references to 3.5 as 3.4 to reflect the currently supported version within the CI test suite (2.7 and 3.5)

CONTRIBUTING.md

@@ -106,7 +106,7 @@ There are three ways to setup an Apache Airflow development environment.
 
 1. Using tools and libraries installed directly on your system.
 
-  Install Python (2.7.x or 3.4.x), MySQL, and libxml by using system-level package
+  Install Python (2.7.x or 3.5.x), MySQL, and libxml by using system-level package
   managers like yum, apt-get for Linux, or Homebrew for Mac OS at first. Refer to the [base CI Dockerfile](https://github.com/apache/incubator-airflow-ci/blob/master/Dockerfile) for
   a comprehensive list of required packages.
 
@@ -267,7 +267,7 @@ meets these guidelines:
 1. Preface your commit's subject & PR's title with **[AIRFLOW-XXX]** where *XXX* is the JIRA number. We compose release notes (i.e. for Airflow releases) from all commit titles in a release. By placing the JIRA number in the commit title and hence in the release notes, Airflow users can look into JIRA and Github PRs for more details about a particular change.
 1. Add an [Apache License](http://www.apache.org/legal/src-headers.html) header to all new files
 1. If the pull request adds functionality, the docs should be updated as part of the same PR. Doc string are often sufficient.  Make sure to follow the Sphinx compatible standards.
-1. The pull request should work for Python 2.7 and 3.4. If you need help writing code that works in both Python 2 and 3, see the documentation at the [Python-Future project](http://python-future.org) (the future package is an Airflow requirement and should be used where possible).
+1. The pull request should work for Python 2.7 and 3.5. If you need help writing code that works in both Python 2 and 3, see the documentation at the [Python-Future project](http://python-future.org) (the future package is an Airflow requirement and should be used where possible).
 1. As Airflow grows as a project, we try to enforce a more consistent style and try to follow the Python community guidelines. We track this using [landscape.io](https://landscape.io/github/apache/incubator-airflow/), which you can setup on your fork as well to check before you submit your PR. We currently enforce most [PEP8](https://www.python.org/dev/peps/pep-0008/) and a few other linting rules. It is usually a good idea to lint locally as well using [flake8](https://flake8.readthedocs.org/en/latest/) using `flake8 airflow tests`. `git diff upstream/master -u -- "*.py" | flake8 --diff` will return any changed files in your branch that require linting.
 1. Please read this excellent [article](http://chris.beams.io/posts/git-commit/) on commit messages and adhere to them. It makes the lives of those who come after you a lot easier.
 

setup.py

@@ -399,7 +399,6 @@ def do_setup():
             'Intended Audience :: System Administrators',
             'License :: OSI Approved :: Apache Software License',
             'Programming Language :: Python :: 2.7',
-            'Programming Language :: Python :: 3.4',
             'Programming Language :: Python :: 3.5',
             'Topic :: System :: Monitoring',
         ],
@@ -413,7 +412,7 @@ def do_setup():
             'extra_clean': CleanCommand,
             'compile_assets': CompileAssets
         },
-        python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*',
+        python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*',
     )