Fix pyang version in setup.py

Change-Id: Idc1599d156b17a9014333c8b68a19d65cc436210
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/setup.py b/setup.py
index e32360b..4cd2be2 100644
--- a/setup.py
+++ b/setup.py
@@ -30,7 +30,7 @@
         subprocess.call([sys.executable, "-m", "pip", "install", package])
 
     def run(self):
-        self.pipinstall('pyang==6.0.1')
+        self.pipinstall('pyang==2.5.3')
         self.pipinstall('pyangbind==0.8.3.post1')
         import pyangbind
         print("Using dir {}/{} for python artifacts".format(os.getcwd(), self.im_dir))