Ignore JMH 1.21 release

The 1.19 release was added to pom-scijava very recently.
Let's not rock the boat with an upgrade yet.

Author: ctrueden

timestamps.txt

@@ -52,6 +52,8 @@ org.jetbrains.kotlin:kotlin-stdlib-jdk8 20181026000000
 org.jmockit:jmockit 20190101120000
 org.mockito:mockito-core 20181026000000
 org.ojalgo:ojalgo 20181026000000
+org.openjdk.jmh:jmh-core 20181026000000
+org.openjdk.jmh:jmh-generator-annprocess 20181026000000
 org.scijava:batch-processor 20181016000000
 org.scijava:j3dcore 20180905120000
 org.scijava:j3dutils 20180905120000