Update Transifex slug for 29.x

Update the Transifex slug to match the new resource created for the
upcoming 29.x branch.

Author: hebasto

.tx/config

@@ -1,7 +1,7 @@
 [main]
 host = https://www.transifex.com
 
-[o:bitcoin:p:bitcoin:r:qt-translation-028x]
+[o:bitcoin:p:bitcoin:r:qt-translation-029x]
 file_filter = src/qt/locale/bitcoin_<lang>.xlf
 source_file = src/qt/locale/bitcoin_en.xlf
 source_lang = en