Set path_style for S3 bucket name with dots

Recently I updated my fog bundled version and got errors when syncing assets. After digging to the codes, I found several discussions about S3 bucket name with dots included. Ref: fog/fog#2381 

Adding `:path_style= > true` for `fog_options` when `fog_directory` contains dots would fix this issue.

This pul request closes #237.