Fix collections deprecation warning

```python
ifcopenshell/geom/occ_utils.py:28ifcopenshell/geom/occ_utils.py:28
  /home/cyril/git/BIMxBEM/ifcopenshell/geom/occ_utils.py:28: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3, and in 3.9 it will stop working
    from collections import namedtuple, Iterable
```

src/ifcblenderexport/occ_utils.py

@@ -25,7 +25,11 @@ import random
 import operator
 import warnings
 
-from collections import namedtuple, Iterable
+from collections import namedtuple
+try:  # python 3.3+
+    from collections.abc import Iterable
+except ModuleNotFoundError: # python 2
+    from collections import Iterable
 
 try:
     from OCC.Core import TopoDS, gp, Quantity, BRepTools 

src/ifcopenshell-python/ifcopenshell/geom/app.py

@@ -11,7 +11,11 @@ import multiprocessing
 
 import OCC.AIS
 
-from collections import defaultdict, Iterable, OrderedDict
+from collections import defaultdict, OrderedDict
+try:  # python 3.3+
+    from collections.abc import Iterable
+except ModuleNotFoundError: # python 2
+    from collections import Iterable
 
 try:
     QString = unicode

src/ifcopenshell-python/ifcopenshell/geom/occ_utils.py

@@ -25,7 +25,11 @@ import random
 import operator
 import warnings
 
-from collections import namedtuple, Iterable
+from collections import namedtuple
+try:  # python 3.3+
+    from collections.abc import Iterable
+except ModuleNotFoundError: # python 2
+    from collections import Iterable
 
 try:
     from OCC.Core import V3d, TopoDS, gp, AIS, Quantity, BRepTools, Graphic3d