Fix typo

README.md

@@ -55,7 +55,7 @@ For a more detailed guide, please refer to our
 
     ```shell
     # Nordic nRF52840-DK board
-    ./deploy.py os --board=nrf52840dk
+    ./deploy.py os --board=nrf52840_dk
     # Nordic nRF52840-Dongle
     ./deploy.py os --board=nrf52840_dongle
     ```

docs/install.md

@@ -145,7 +145,7 @@ Our build script `build.rs` is responsible for converting `opensk_cert.pem` and
     differ_):
 
     ```shell
-    $ ./deploy.py os --board=nrf52840_dongle
+    $ ./deploy.py os --board=nrf52840_dk
         info: Updating rust toolchain to nightly-2020-02-03
         info: syncing channel updates for 'nightly-2020-02-03-x86_64-unknown-linux-gnu'
         info: checking for self-updates