Fix picard heapspace error in align rule

In the Singularity image for picard, the default heapsize is too small,
leading to crashes in the pipeline when the rule 'align' runs out of
heap space. The solution is to explicitly specify the heap space that
picard can use, thereby overriding the default value that is set in the
Singularity image.

This issue was reported on capture-lumc-wrapper, see
https://git.lumc.nl/klinische-genetica/capture-lumc/capture-lumc-wrapper/issues/26
for details.
6 jobs for hotfix-2019-07-17 in 43 seconds (queued for 1 second)
Status Job ID Name Coverage
  Sanity
failed test_sanities #4166
docker

00:00:43

failed test_sanities #4137
docker

00:00:42

failed test_sanities #4161
docker

00:01:41

 
  Dry Run
skipped test_dry_run #4138
docker
 
  Integration
skipped test_integration #4140
slurm
skipped test_integration_singularity #4139
docker
 
Name Stage Failure
failed
test_sanities Sanity
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