Update Dockerfile, use git clone instead of files

Status Job ID Name Coverage
  Linux
failed #365428
BranchJobLinux

00:00:31

failed #365427
BranchJobLinux

00:01:18

failed #365426
BranchJobLinux

00:02:42

 
Name Stage Failure
failed
BranchJobLinux Linux
[ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK?
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
ERROR: Job failed: command terminated with exit code 1