contrib: bump xcb, xcb-proto and xau
For xcb, 1.14 is out since February 2020[¹].
Fixes compilation error such as:
GEN xproto.c
File "$VLC/contrib/contrib-native/libxcb/src/./c_client.py", line 1937
after_end_of_request = '(((char*)R) + R->length * 4)'
TabError: inconsistent use of tabs and spaces in indentation
Edited by Alexandre Janniaux