python: Make the typing module a requirement only for old python versions.

Typing is part of standard library from python 3.5 and from python 3.7
onwards trying to install it results in an error.

This patch disables typing installation on python versions that are
newer than 3.5.

Signed-off-by: Damir Jelić <poljar@termina.org.uk>

python/setup.py

@@ -22,6 +22,10 @@ setup(
     packages=["olm"],
     setup_requires=["cffi>=1.0.0"],
     cffi_modules=["olm_build.py:ffibuilder"],
-    install_requires=["cffi>=1.0.0", "future", "typing"],
+    install_requires=[
+        "cffi>=1.0.0",
+        "future",
+        "typing;python_version<'3.5'"
+    ],
     zip_safe=False
 )