fix(ie11): removes "Array.from()" and "new Set()"

The TypeScript transpilation process polyfills many things,
like the spread operator (...array), or for...of, but it does
not for Array.from and new Set(). This was breaking
behavior in IE11.

src/locale/matchers/LocaleMatcherDefault.ts

@@ -67,10 +67,11 @@ class LocaleMatcherDefault implements Matcher {
 		});
 
 		const converted = candidates
+			.filter((el, i, a) => i === a.indexOf(el)) // deduplicate
 			.map(candidate => Locale.parse(candidate))
 			.filter(l => !l.hasParseError());
 
-		return Array.from(new Set(converted));
+		return converted;
 	}
 }