TST: Test Sphinx 1.6.2 instead of 1.6.1

... because of a bug that was fixed in 16d05695368cdd394110f99af7109212c67faa8c.

Author: mgeier

.travis.yml

@@ -8,7 +8,7 @@ matrix:
   - env: ADDITIONAL_COMMAND="python -m sphinx doc/ doc/_build/ -b linkcheck"
 
   # a few older Sphinx releases using default Python version
-  - env: SPHINX="==1.6.1"
+  - env: SPHINX="==1.6.2"
   - env: SPHINX="==1.6.7"
   - env: SPHINX="==1.7.5"
   - env: SPHINX="==1.8.2"