Merge pull request #49 from AzureAD/conditional-dependency

Use more precise dependency declaration

Author: rayluo

setup.py

@@ -25,7 +25,8 @@
     package_data={'': ['LICENSE']},
     install_requires=[
         'msal>=0.4.1,<2.0.0',
-        'portalocker~=1.6',
+        "portalocker~=1.6;platform_system=='Windows'",
+        "portalocker~=1.0;platform_system!='Windows'",
         "pathlib2;python_version<'3.0'",
         ## We choose to NOT define a hard dependency on this.
         # "pygobject>=3,<4;platform_system=='Linux'",