cannot make cache directory on Windows 10

Identified by user through the help forum here:

https://www.synapse.org/#!Synapse:syn5637528/discussion/threadId=6334

Loading the package fails due to the Synapse cache directory not being able to be created. My suspicion is that this line (https://github.com/Sage-Bionetworks/synapsePythonClient/blob/master/synapseclient/cache.py#L30) is not safe for Windows, as tildes are reserved for other uses (https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file?redirectedfrom=MSDN#short-vs-long-names). Instead, we should use `os.path.expanduser` to get the current users home directory (https://docs.python.org/3.5/library/os.path.html).

I will file this issue for the Python client as well and link it here.

Reminder to follow up in the discussion forum when a fix is known, thanks!