Issue 4490 - Update buildtools dependency

ensure_dependencies.py

 #!/usr/bin/env python
 
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import sys
 import os
 import posixpath
 import re
@@ skipping 202 matching lines @@
             for line in handle:
                 # Remove comments and whitespace
                 line = re.sub(r'#.*', '', line).strip()
                 if not line:
                     continue
 
                 key, spec = parse_spec(deps_path, line)
                 if spec:
                     result[key] = spec
         return result
-    except IOError, e:
+    except IOError as e:
         if e.errno != errno.ENOENT:
             raise
         return None
 
 
 def safe_join(path, subpath):
     # This has been inspired by Flask's safe_join() function
     forbidden = {os.sep, os.altsep} - {posixpath.sep, None}
     if any(sep in subpath for sep in forbidden):
         raise Exception('Illegal directory separator in dependency path %s' % subpath)
@@ skipping 91 matching lines @@
         ensure_repo(repodir, parenttype, target, vcs, _root.get(vcs, ''), source)
         update_repo(target, vcs, rev)
         resolve_deps(target, level + 1, self_update=False,
                      overrideroots=overrideroots, skipdependencies=skipdependencies)
 
     if self_update and '_self' in config and '*' in config['_self']:
         source = safe_join(repodir, config['_self']['*'])
         try:
             with io.open(source, 'rb') as handle:
                 sourcedata = handle.read()
-        except IOError, e:
+        except IOError as e:
             if e.errno != errno.ENOENT:
                 raise
             logging.warning("File %s doesn't exist, skipping self-update" % source)
             return
 
         target = __file__
         with io.open(target, 'rb') as handle:
             targetdata = handle.read()
 
         if sourcedata != targetdata:
@@ skipping 26 matching lines @@
     args = parser.parse_args()
 
     if args.quiet:
         logging.disable(logging.INFO)
 
     repos = args.repos
     if not len(repos):
         repos = [os.path.dirname(__file__)]
     for repo in repos:
         resolve_deps(repo)