flake8 . --show-source gives us more context

* Trusty and sudo false are now th defaults
* Add pip caching of modules will speed up Travis builds
* Step up to Python 3.6

.travis.yml

@@ -1,20 +1,16 @@
-sudo: false
-dist: trusty
 language: python
 python:
-    - 3.5        # currently Travis trusty default Python3 is 3.5.2
-    #- 3.6.1
-    #- "nightly"  # currently points to 3.7-dev (3.7.0a0)
+    - 3.6
+cache: pip
 install:
     - pip install flake8 pytest
 before_script:
     # stop the build if there are Python syntax errors or undefined names
-    - flake8 . --count --select=E901,E999,F821,F822,F823 --statistics
+    - flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics
     # exit-zero treates all errors as warnings.  The GitHub editor is 127 chars wide
     - flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
 script:
     pytest --capture=sys
-    # python unittest.py
 notifications:
     on_success: change
     on_failure: change  # `always` will be the setting once code changes slow down