remove return outside of function as it not es6 module compliant

index.js

@@ -3,40 +3,39 @@
 var $Map = typeof Map === 'function' && Map.prototype ? Map : null;
 var $Set = typeof Set === 'function' && Set.prototype ? Set : null;
 
-if (!$Map) {
-	// eslint-disable-next-line no-unused-vars
+if ($Map) {
+	var $mapHas = $Map ? Map.prototype.has : null;
+	var $setHas = $Set ? Set.prototype.has : null;
+	if (!$mapHas) {
+		// eslint-disable-next-line no-unused-vars
+		module.exports = function isMap(x) {
+			// `Map` does not have a `has` method
+			return false;
+		};
+		return;
+	}
+
 	module.exports = function isMap(x) {
-		// `Map` is not present in this environment.
+		if (!x || typeof x !== 'object') {
+			return false;
+		}
+		try {
+			$mapHas.call(x);
+			if ($setHas) {
+				try {
+					$setHas.call(x);
+				} catch (e) {
+					return true;
+				}
+			}
+			return x instanceof $Map; // core-js workaround, pre-v2.5.0
+		} catch (e) {}
 		return false;
 	};
-	return;
-}
-
-var $mapHas = $Map ? Map.prototype.has : null;
-var $setHas = $Set ? Set.prototype.has : null;
-if (!$mapHas) {
+} else {
 	// eslint-disable-next-line no-unused-vars
 	module.exports = function isMap(x) {
-		// `Map` does not have a `has` method
+	// `Map` is not present in this environment.
 		return false;
 	};
-	return;
 }
-
-module.exports = function isMap(x) {
-	if (!x || typeof x !== 'object') {
-		return false;
-	}
-	try {
-		$mapHas.call(x);
-		if ($setHas) {
-			try {
-				$setHas.call(x);
-			} catch (e) {
-				return true;
-			}
-		}
-		return x instanceof $Map; // core-js workaround, pre-v2.5.0
-	} catch (e) {}
-	return false;
-};