Adding libcanberra-gtk-module to fix a crash when running this Dockerfile on unbuntu 14.04
```
root@fb9f5404a971:/# firefox
(firefox:5): Gtk-WARNING **: Locale not supported by C library.
Using the fallback 'C' locale.
Gtk-Message: Failed to load module "canberra-gtk-module"
[5] ###!!! ABORT: X_ShmPutImage: BadValue (integer parameter out of range for operation); 9 requests ago: file /builds/slave/rel-m-rel-l64_bld-000000000000/build/toolkit/xre/nsX11ErrorHandler.cpp, line 157
[5] ###!!! ABORT: X_ShmPutImage: BadValue (integer parameter out of range for operation); 9 requests ago: file /builds/slave/rel-m-rel-l64_bld-000000000000/build/toolkit/xre/nsX11ErrorHandler.cpp, line 157
root@fb9f5404a971:/#
(process:36): Gtk-WARNING **: Locale not supported by C library.
Using the fallback 'C' locale.
Gtk-Message: Failed to load module "canberra-gtk-module"
```
