Mark repo2docker as requiring at least Python 3.4

And test with 3.4 on Travis.

.travis.yml

@@ -3,7 +3,7 @@ sudo: required
 services:
   - docker
 python:
-  - 3.5
+  - 3.4
 
 install:
   - pip install -e .

setup.py

@@ -4,7 +4,7 @@ from setuptools import setup, find_packages
 
 setup(
     name='jupyter-repo2docker',
-    version='0.2.10',
+    version='0.3',
     install_requires=[
         'docker',
         'traitlets',
@@ -12,13 +12,14 @@ setup(
         'escapism',
         'jinja2'
     ],
+    python_requires='>=3.4',
     author='Yuvi Panda',
     author_email='yuvipanda@gmail.com',
     license='BSD',
     packages=find_packages(),
     entry_points={
         'console_scripts': [
-            'jupyter-repo2docker = repo2docker.__main__:main'
+            'jupyter-repo2docker = repo2docker.__main__:main',
         ]
     },
 )