Determine if an upper bound on `decorator` version is needed for networkx <=2.5

[chenghlee]

NetworkX 2.5.1 introduced an upper bound on decorator:

$ git log -1 --patch 36383ccc9
commit 36383ccc94a2e2d50893e13bb2a3ec96e5f6518f (HEAD, tag: networkx-2.5.1, origin/v2.5)
Author: Jarrod Millman <jarrod.millman@gmail.com>
Date:   Sat Apr 3 15:07:32 2021 -0700

    Pin upper bound of decorator dep.

diff --git a/networkx/release.py b/networkx/release.py
index 675b13e4..0476b940 100644
--- a/networkx/release.py
+++ b/networkx/release.py
@@ -171,7 +171,7 @@ def get_info(dynamic=True):
 # Version information
 name = "networkx"
 major = "2"
-minor = "5"
+minor = "5.1"

 # Declare current release as a development release.
diff --git a/requirements/default.txt b/requirements/default.txt
index 570c163c..92d735a2 100644
--- a/requirements/default.txt
+++ b/requirements/default.txt
@@ -1 +1 @@
-decorator>=4.3.0
+decorator>=4.3,<5
diff --git a/setup.py b/setup.py
index 398b3d99..eb1521d7 100644
--- a/setup.py
+++ b/setup.py
@@ -124,7 +124,7 @@ package_data = {
     "networkx.utils": ["tests/*.py"],
 }

-install_requires = ["decorator>=4.3.0"]
+install_requires = ["decorator>=4.3,<5"]
 extras_require = {
     "all": [
         "numpy",

This strongly suggests that newer versions of the decorator package may not be compatible with older versions of networkx.