Updated configuration for Pelican 3.5

- Added ASSET_SOURCE_PATHS setting to fix Assets plugin
- Removed SmartyPants from requirements.txt (it is installed as a
dependency of Typogrify)
- Added `.DS_Store` to IGNORE_FILES setting

Generated by commit 872a2b3a52a6572e9951394dc9504b05e6c59867; pushed by Travis build 86.