Update license year in NOTICE.txt

qwwdfsad · yorickhenning · commit 91188eaac29d · 2021-10-14T00:14:50.000Z
Fixes Kotlin#2934
diff --git a/license/NOTICE.txt b/license/NOTICE.txt
@@ -5,4 +5,4 @@
 =========================================================================
 
 kotlinx.coroutines library.
-Copyright 2016-2019 JetBrains s.r.o and respective authors and developers
+Copyright 2016-2021 JetBrains s.r.o and respective authors and developers
