Add a redirect from cbk-zam to cbk (#119)

Other Chavacano varieties don't have codes. The have very few speakers,
and aren't expected to be used distinctly. In such cases we usually
redirect the specific code to a general standard code.

Addresses downstream bug:
https://phabricator.wikimedia.org/T263717

data/language-data.json

@@ -616,13 +616,16 @@
             ],
             "Kaqchikel"
         ],
-        "cbk-zam": [
+        "cbk": [
             "Latn",
             [
                 "AS"
             ],
             "Chavacano de Zamboanga"
         ],
+        "cbk-zam": [
+            "cbk"
+        ],
         "ccp": [
             "Cakm",
             [