Fix loading of Lato font in style.css for docs

Hello Steve,

The "@import url()" statement for loading Lato from Google Fonts
was ignored because "@import are not allowed after any valid statement
other than @charset and @import" according to the W3C CSS Validator,
so I moved the @import statement to the very top.

Also, the latest Lato font on Google seems to have some of its font weights
adjusted, so the @import line has been updated accordingly.

There also used to be `@import url(line-icons.css)`, but the file isn't found
in the git repository.  I presume that line-icons.css has been replaced
with the use of FontAwesome?  :-)

Thank you for creating Hugo.  It has been fun learning it.