fix redundancy or copy & paste typo
Cross compilation instructions contained `gcc` dependency two times, but it should certainly be `gcc` and `g++` instead.
@@ -89,13 +89,13 @@ $ sudo apt update
If you use `cargo` from the repository
```bash
-$ sudo apt install gcc-aarch64-linux-gnu gcc-aarch64-linux-gnu libc6-dev:arm64 libstd-rust-dev:arm64
+$ sudo apt install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu libc6-dev:arm64 libstd-rust-dev:arm64
```
If you use Rustup:
```bash
-$ sudo apt install gcc-aarch64-linux-gnu gcc-aarch64-linux-gnu libc6-dev:arm64
+$ sudo apt install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu libc6-dev:arm64
$ rustup target add aarch64-unknown-linux-gnu
```
