install picard-2.6.0

Hi,

I have a trouble with installing picard-2.6.0.
When I execute the command ./gradlew, the result shows the below.

FAILURE: Build failed with an exception.

• Where:
  Build file '/opt/broadinstitute-picard-679ea0d/build.gradle' line: 20

• What went wrong:
  An exception occurred applying plugin request [id: 'org.ajoberstar.grgit', version:

  Failed to apply plugin [id 'org.ajoberstar.grgit']
  One of setGitDir or setWorkTree must be called.

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug opti

  BUILD FAILED

  How do I solve the problem?
  Thanks.