Bump groovy in /net.tascalate.javaflow.tools.gradle

Bumps [groovy](https://github.com/apache/groovy) from 2.4.15 to 2.4.21. - [Release notes](https://github.com/apache/groovy/releases) - [Commits](https://github.com/apache/groovy/commits) --- updated-dependencies: - dependency-name: org.codehaus.groovy:groovy dependency-type: direct:production ... Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

net.tascalate.javaflow.tools.gradle/pom.xml

@@ -50,7 +50,7 @@
 <dependency>
 <groupId>org.codehaus.groovy</groupId>
 <artifactId>groovy</artifactId>
-<version>2.4.15</version>
+<version>2.4.21</version>
 <scope>provided</scope>
 </dependency>