examples: fix print of error message

examples/display-shapes.py

@@ -37,14 +37,14 @@ try:
     viz.initViewer()
 except ImportError as error:
     print("Error while initializing the viewer. It seems you should install gepetto-viewer")
-    print(error.message)
+    print(error)
     sys.exit(0)
 
 try:
     viz.loadViewerModel("shapes")
 except AttributeError as error:
     print("Error while loading the viewer model. It seems you should start gepetto-viewer")
-    print(error.message)
+    print(error)
     sys.exit(0)
 
 viz.display(np.zeros(0))