[Gradle, JS] Remove trailing commas from webpack config

#KT-39377 fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpackConfig.kt

@@ -218,8 +218,8 @@ data class KotlinWebpackConfig(
                 });
                 config.devtool = ${devtool?.let { "'$it'" } ?: false};
                 config.stats = {
-                    warningsFilter: [/Failed to parse source map/],
-                },
+                    warningsFilter: [/Failed to parse source map/]
+                }
                 
             """.trimIndent()
         )