[Fix] Fix errors about in operator.

The in operator can only be used to check if a property is in an object. You can't search in strings, or in numbers, or other primitive types.
See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/in_operator_no_object#What_went_wrong

Author: linkeo

index.js

@@ -4,7 +4,7 @@ var hasToStringTag = typeof Symbol === 'function' && typeof Symbol.toStringTag =
 var toStr = Object.prototype.toString;
 
 var isStandardArguments = function isArguments(value) {
-	if (hasToStringTag && value && Symbol.toStringTag in value) {
+	if (hasToStringTag && value && typeof value === 'object' && Symbol.toStringTag in value) {
 		return false;
 	}
 	return toStr.call(value) === '[object Arguments]';

test.js

@@ -7,7 +7,8 @@ var hasToStringTag = typeof Symbol === 'function' && typeof Symbol.toStringTag =
 test('primitives', function (t) {
 	t.notOk(isArguments([]), 'array is not arguments');
 	t.notOk(isArguments({}), 'object is not arguments');
-	t.notOk(isArguments(''), 'string is not arguments');
+	t.notOk(isArguments(''), 'empty string is not arguments');
+	t.notOk(isArguments('foo'), 'string is not arguments');
 	t.notOk(isArguments({ length: 2 }), 'naive array-like is not arguments');
 	t.end();
 });