Change Sydney bitdevs (#193)

Sydney now has a bitdevs meet separate to the regular meetup. Its a
subset of the same crew and there are good relations between everyone
involved.

Seeing as this is the bitdevs page not the Bitcoin Meetups page link to
the Sydney bitdevs website instead of meetup.com where the Sydney
Bitcoin organises themselves.

Author: tcharding

cities.md

@@ -46,7 +46,7 @@ As a disclaimer, BitDevs NYC has no official associations with or oversight of t
 - [São Paulo](https://bitdevsportugues.org)
 - [Seattle](https://github.com/reardencode/seattle_bitdevs)
 - [Singapore](https://bitdevs.sg/)
-- [Sydney](https://www.meetup.com/bitcoin_sydney/)
+- [Sydney](https://sydney.bitdevs.com.au/)
 - [Taipei](https://bitdevs.tw/)
 - [Tampa](https://tampabitdevs.io/)
 - [Vancouver](https://bitdevs.ca/)