feat(nested): gdcdatamodel support nested subgroup

Author: thanh-nguyen-dang

requirements.txt

@@ -31,7 +31,7 @@ psqlgraph==1.2.3
 -e git+https://git@github.com/uc-cdis/cdislogging.git@master#egg=cdislogging
 -e git+https://git@github.com/NCI-GDC/cdisutils.git@f54e393c89939b2200dfae45c6235cbe2bae1206#egg=cdisutils
 -e git+https://git@github.com/uc-cdis/datadictionary.git@0.2.1#egg=gdcdictionary
-gdcdatamodel==1.3.9
+-e git+https://git@github.com/uc-cdis/gdcdatamodel.git@db3721ff0bab682015b3df45b1c8e79cc136c31c#egg=gdcdatamodel
 -e git+https://git@github.com/uc-cdis/indexclient.git@1.5.7#egg=indexclient
 -e git+https://git@github.com/NCI-GDC/python-signpostclient.git@ca686f55772e9a7f839b4506090e7d2bb0de5f15#egg=signpostclient
 -e git+https://git@github.com/uc-cdis/storage-client.git@0.1.7#egg=storageclient