setup: use more flexible networkx reqs

https://github.com/iterative/dvc/commit/50fc721811a015142b476e90f8d198a99e88892f

setup.py

@@ -49,7 +49,6 @@ class build_py(_build_py):
 
 
 install_requires = [
-    "networkx>=2.1,<2.3",
     "ply>=3.9",  # See https://github.com/pyinstaller/pyinstaller/issues/1945
     "configparser>=3.5.0",
     "future>=0.16.0",
@@ -79,6 +78,11 @@ install_requires = [
     "win-unicode-console>=0.5; sys_platform == 'win32'",
 ]
 
+if sys.version_info[0] == 2:
+    install_requires.append("networkx>=2.1,<2.3")
+else:
+    install_requires.append("networkx>=2.1,<2.4")
+
 # Extra dependencies for remote integrations
 
 gs = ["google-cloud-storage==1.19.0"]