require Python 3.5

3.4 doesn't have isawaitable

remove unsupported combinations from test matrix

Author: minrk

.travis.yml

@@ -93,20 +93,13 @@ matrix:
           - MOZ_HEADLESS=1
           addons:
             firefox: 57.0
-
-        - python: 3.4
-          env: GROUP=python
         - python: 3.5
           env: GROUP=python
         - python: 3.7
           dist: xenial
           env: GROUP=python
         - python: 3.6
           env: GROUP=docs
-        - python: 3.6
-          env:
-          - GROUP=python
-          - EXTRA_PIP="tornado<5"
 
 after_success:
     - codecov

setup.py

@@ -120,7 +120,7 @@
                  'nbval', 'nose-exclude', 'selenium', 'pytest', 'pytest-cov'],
         'test:sys_platform == "win32"': ['nose-exclude'],
     },
-    python_requires = '>=3.4', 
+    python_requires = '>=3.5',
     entry_points = {
         'console_scripts': [
             'jupyter-notebook = notebook.notebookapp:main',