Take into account the confidence of language.Matcher

I had a weird but that sometimes the application would use Spanish as
the default language, even though the user had not passed Spanish as
value of the Accept-Language header and the default is hard-coded to
Catalan.

I learned that language.Matcher **always** returns one of its defined
locales, even if there is no way to match the passed list of languages
to Match.  In that case, it returns a confidence of “No”, meaning that
the match failed.

Usually go the default Catalan locale because most of the time this was
set as the first language to Matcher, but since Go randomizes maps,
there were times that Spanish was first.

pkg/locale/locale.go

@@ -68,13 +68,15 @@ func Match(acceptLanguage string, locales Locales, matcher language.Matcher) *Lo
 		return nil
 	}
 	var locale *Locale
-	tag, _, _ := matcher.Match(t...)
+	tag, _, confidence := matcher.Match(t...)
+	if confidence > language.No {
 		var ok bool
 		locale, ok = locales[tag]
 		for !ok && !tag.IsRoot() {
 			tag = tag.Parent()
 			locale, ok = locales[tag]
 		}
+	}
 	return locale
 }