commands: Fix golint issues

commands/hugo.go:65:1: exported method Response.IsUserError should have comment or be unexported
commands/import_jekyll.go💯21: error strings should not be capitalized or end with punctuation or a newline
commands/server.go:417:1: receiver name sc should be consistent with previous receiver name s for serverCmd

commands/hugo.go

@@ -62,6 +62,8 @@ type Response struct {
 	Cmd *cobra.Command
 }
 
+// IsUserError returns true is the Response error is a user error rather than a
+// system error.
 func (r Response) IsUserError() bool {
 	return r.Err != nil && isUserError(r.Err)
 }