Update to Kotlin 1.4.21 (#2473)

diff --git a/README.md b/README.md
index 2b9adc0..c3da938 100644
--- a/README.md
+++ b/README.md
@@ -3,11 +3,11 @@
 [![official JetBrains project](https://jb.gg/badges/official.svg)](https://confluence.jetbrains.com/display/ALL/JetBrains+on+GitHub)
 [![GitHub license](https://img.shields.io/badge/license-Apache%20License%202.0-blue.svg?style=flat)](https://www.apache.org/licenses/LICENSE-2.0)
 [![Download](https://api.bintray.com/packages/kotlin/kotlinx/kotlinx.coroutines/images/download.svg?version=1.4.2) ](https://bintray.com/kotlin/kotlinx/kotlinx.coroutines/1.4.2)
-[![Kotlin](https://img.shields.io/badge/kotlin-1.4.20-blue.svg?logo=kotlin)](http://kotlinlang.org)
+[![Kotlin](https://img.shields.io/badge/kotlin-1.4.21-blue.svg?logo=kotlin)](http://kotlinlang.org)
 [![Slack channel](https://img.shields.io/badge/chat-slack-green.svg?logo=slack)](https://kotlinlang.slack.com/messages/coroutines/)
 
 Library support for Kotlin coroutines with [multiplatform](#multiplatform) support.
-This is a companion version for Kotlin `1.4.20` release.
+This is a companion version for Kotlin `1.4.21` release.
 
 ```kotlin
 suspend fun main() = coroutineScope {
@@ -95,7 +95,7 @@
 
 ```xml
 <properties>
-    <kotlin.version>1.4.20</kotlin.version>
+    <kotlin.version>1.4.21</kotlin.version>
 </properties>
 ```
 
@@ -113,7 +113,7 @@
 
 ```groovy
 buildscript {
-    ext.kotlin_version = '1.4.20'
+    ext.kotlin_version = '1.4.21'
 }
 ```
 
@@ -139,7 +139,7 @@
 
 ```groovy
 plugins {
-    kotlin("jvm") version "1.4.20"
+    kotlin("jvm") version "1.4.21"
 }
 ```
 
diff --git a/gradle.properties b/gradle.properties
index f92e982..3e055eb 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -5,7 +5,7 @@
 # Kotlin
 version=1.4.2-SNAPSHOT
 group=org.jetbrains.kotlinx
-kotlin_version=1.4.20
+kotlin_version=1.4.21
 
 # Dependencies
 junit_version=4.12
diff --git a/js/example-frontend-js/build.gradle b/js/example-frontend-js/build.gradle
index 2bba602..7abde63 100644
--- a/js/example-frontend-js/build.gradle
+++ b/js/example-frontend-js/build.gradle
@@ -31,24 +31,3 @@
         }
     }
 }
-
-
-// Workaround for bug in 1.4.20 that will be fixed in 1.4.21, KT-43668
-tasks.withType(org.jetbrains.kotlin.gradle.targets.js.npm.tasks.KotlinPackageJsonTask) {
-    doFirst {
-        def producerField = it.class.superclass.getDeclaredMethod("getProducer")
-        producerField.setAccessible(true);
-        def producer = producerField.invoke(it)
-        def items = producer.fileCollectionDependencies
-        def list2 = new HashSet<FileCollectionDependency>()
-        for (FileCollectionDependency item : items) {
-            for (File file : item.files) {
-                if (!file.isFile()) {
-                    list2.add(item)
-                    break
-                }
-            }
-        }
-        items.removeAll(list2)
-    }
-}