integration: Update cargo-xbuild to 0.6.2

The newer version of Rust (after 2020-07-30) requires the latest
cargo-xbuild v0.6.2[1].

[1]
rust-osdev/cargo-xbuild@400592f

Signed-off-by: Akira Moroo <[email protected]>

Author: retrage

run_integration_tests.sh

@@ -3,7 +3,7 @@ set -xeuf
 
 source "${CARGO_HOME:-$HOME/.cargo}/env"
 
-XBUILD_VERSION="0.5.34"
+XBUILD_VERSION="0.6.2"
 cargo install cargo-xbuild --version $XBUILD_VERSION
 
 rustup component add rust-src