test: add arrow functions to test-util-inspect

Even though arrow functions and ES5 anonymous functions are technically
the same for util.js, it won't hurt to test both.  The same goes for
async functions.

test/parallel/test-util-inspect.js

@@ -9,7 +9,9 @@ assert.strictEqual(util.inspect(false), 'false');
 assert.strictEqual(util.inspect(''), "''");
 assert.strictEqual(util.inspect('hello'), "'hello'");
 assert.strictEqual(util.inspect(function() {}), '[Function]');
+assert.strictEqual(util.inspect(() => {}), '[Function]');
 assert.strictEqual(util.inspect(async function() {}), '[AsyncFunction]');
+assert.strictEqual(util.inspect(async () => {}), '[AsyncFunction]');
 assert.strictEqual(util.inspect(function*() {}), '[GeneratorFunction]');
 assert.strictEqual(util.inspect(undefined), 'undefined');
 assert.strictEqual(util.inspect(null), 'null');
@@ -30,8 +32,11 @@ assert.strictEqual(util.inspect([1, [2, 3]]), '[ 1, [ 2, 3 ] ]');
 assert.strictEqual(util.inspect({}), '{}');
 assert.strictEqual(util.inspect({a: 1}), '{ a: 1 }');
 assert.strictEqual(util.inspect({a: function() {}}), '{ a: [Function: a] }');
+assert.strictEqual(util.inspect({a: () => {}}), '{ a: [Function: a] }');
 assert.strictEqual(util.inspect({a: async function() {}}),
                    '{ a: [AsyncFunction: a] }');
+assert.strictEqual(util.inspect({a: async () => {}}),
+                   '{ a: [AsyncFunction: a] }');
 assert.strictEqual(util.inspect({a: function*() {}}),
                    '{ a: [GeneratorFunction: a] }');
 assert.strictEqual(util.inspect({a: 1, b: 2}), '{ a: 1, b: 2 }');