Update nextflow version

.gitlab-ci.yml

 before_script:
   - module add  python/3.6.1-2-anaconda
   - pip install --user pytest-pythonpath==0.7.1 pytest-cov==2.5.1
-  - module load nextflow/0.31.0
+  - module load nextflow/20.01.0
   - ln -s /project/shared/bicf_workflow_ref/workflow_testdata/chipseq/*fastq.gz test_data/
 
 stages: