samples: boards: nrf: battery: fix board in sample commands

The board name used in the zephyr-app-commands directive was the old
name for the Thingy52 board.

Signed-off-by: Gerard Marull-Paretas <[email protected]>

Author: gmarull

samples/boards/nrf/battery/README.rst

@@ -73,7 +73,7 @@ The code can be found in :zephyr_file:`samples/boards/nrf/battery`.
 
 .. zephyr-app-commands::
    :zephyr-app: samples/boards/nrf/battery
-   :board: nrf52_pca20020
+   :board: thingy52_nrf52832
    :goals: build flash
    :compact: