Bump kotlin-stdlib from 1.6.20 to 1.6.21 (#482)

Bumps [kotlin-stdlib](https://github.com/JetBrains/kotlin) from 1.6.20 to 1.6.21.
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pom.xml

@@ -123,7 +123,7 @@
     <guava.version>30.1.1-jre</guava.version>
     <chalk.version>1.0.2</chalk.version>
     <google-collections.version>1.0</google-collections.version>
-    <kotlin.version>1.6.20</kotlin.version>
+    <kotlin.version>1.6.21</kotlin.version>
     <!-- Maven Dependencies -->
     <maven-compiler.version>3.10.1</maven-compiler.version>
     <maven-source.version>3.2.1</maven-source.version>