wiki: devices: Promote dre to 21

Change-Id: I0209f9bde568bd665c13cd1d7eff89cf57a4eb0b

Author: tangalbert919

_data/devices/dre.yml

@@ -13,7 +13,7 @@ codename: dre
 cpu: Kryo 460
 cpu_cores: '8'
 cpu_freq: 2 x 2.0 GHz + 6 x 1.8 GHz
-current_branch: 20
+current_branch: 21
 dimensions: {depth: 8.3, height: 163.1, width: 74.9}
 download_boot: With the device powered off, hold <kbd>Volume Up</kbd> + <kbd>Volume Down</kbd> + <kbd>Power</kbd>.
 firmware_update: firmware_update_oplus_sm4350
@@ -40,5 +40,5 @@ tree: android_device_oneplus_dre
 type: phone
 vendor: OnePlus
 vendor_short: oneplus
-versions: [19.1, 20]
+versions: [19.1, 20, 21]
 wifi: 802.11 a/b/g/n/ac