always use https google font urls (closes #382)

css/theme/beige.css

css/theme/default.css

css/theme/moon.css

css/theme/night.css

css/theme/serif.css

css/theme/simple.css

css/theme/sky.css

css/theme/solarized.css

css/theme/source/beige.scss

css/theme/source/default.scss

css/theme/source/moon.scss

css/theme/source/night.scss

css/theme/source/simple.scss

css/theme/source/sky.scss

css/theme/source/solarized.scss