Check for error value in url.Parse

I noticed I get a panic when running openring with http://antirez.com/rss
The panic happened because the url.Parse returned error is not assigned
to a variable.

    <antirez>
    panic: runtime error: invalid memory address or nil pointer dereference
    [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1119fd6]

    goroutine 1 [running]:
    net/url.(*URL).ResolveReference(0xc0004c0bd0, 0x0, 0x0)
            /usr/local/Cellar/go/1.16.5/libexec/src/net/url/url.go:1075 +0x36
    main.main()
            /Users/gianarb/git/openring/openring.go:152 +0x9c

There is another problem, the URL is not valid for the url.Parse
function for some reason. But this is an issue for another day.

Signed-off-by: Gianluca Arbezzano <ciao@gianarb.it>

openring.go

@@ -130,7 +130,7 @@ func main() {
 		if err != nil {
 			log.Fatal("failed parsing update URL of the feed")
 		}
-		feedLink, _ := url.Parse(feed.Link)
+		feedLink, err := url.Parse(feed.Link)
 		if err != nil {
 			log.Fatal("failed parsing canonical feed URL of the feed")
 		}