在centos上运行dcos 1.8。我安装了cli，如下所示：https://docs.mesosphere.com/1.8/usage/cli/install/
当我试图做一个Spark安装我得到以下错误。有什么想法吗？

./dcos package install spark
ip-172-16-6-6.localdomain's username: admin
admin@ip-172-16-6-6.localdomain's password:
Traceback (most recent call last):
 File "cli/dcoscli/subcommand.py", line 99, in run_and_capture
 File "cli/dcoscli/package/main.py", line 21, in main
 File "cli/dcoscli/util.py", line 21, in wrapper
 File "cli/dcoscli/package/main.py", line 35, in _main
 File "dcos/cmds.py", line 43, in execute
 File "cli/dcoscli/package/main.py", line 356, in _install
 File "dcos/cosmospackage.py", line 191, in get_package_version
 File "dcos/cosmospackage.py", line 366, in __init__
 File "cli/env/lib/python3.4/site-packages/requests/models.py", line 826, in       json
 File "json/__init__.py", line 318, in loads
 File "json/decoder.py", line 343, in decode
 File "json/decoder.py", line 361, in raw_decode
 ValueError: Expecting value: line 1 column 1 (char 0)