Drop 2.6, 3.3 from travis at least.

Most other bits in the ecosystem, now including stuff like Releases,
officially don't support 2.6/3.3 anymore. Not yet willing to make
the official cut here, but we can at least keep it from causing
test fails.

Author: bitprophet

.travis.yml

@@ -1,9 +1,7 @@
 language: python
 cache: pip
 python:
-  - "2.6"
   - "2.7"
-  - "3.3"
   - "3.4"
   - "3.5"
   - "3.6"
@@ -14,18 +12,6 @@ env:
   - SPHINX=">=1.4,<1.5"
   - SPHINX=">=1.5,<1.6"
   - SPHINX=">=1.6,<1.7"
-matrix:
-  exclude:
-    # Sphinx dropped Python 2.6 support in version 1.5
-    - python: "2.6"
-      env: SPHINX=">=1.5,<1.6"
-    - python: "2.6"
-      env: SPHINX=">=1.6,<1.7"
-    # And they dropped Python 3.3 support at some point too.
-    - python: "3.3"
-      env: SPHINX=">=1.5,<1.6"
-    - python: "3.3"
-      env: SPHINX=">=1.6,<1.7"
 install:
   # For some reason Travis' build envs have wildly different pip/setuptools
   # versions between minor Python versions, and this can cause many hilarious