Use nightly to test documentation

ci.sh

@@ -7,6 +7,18 @@ has_target() {
 ensure_target() {
  has_target "$1" || rustup target add "$1"
 }
+
+ensure_target thumbv7em-none-eabi
+
+has_toolchain() {
+ rustup toolchain list | grep -q "$1"
+}
+ensure_toolchain() {
+ has_toolchain "$1" || rustup toolchain install "$1"
+}
+
+ensure_toolchain nightly-x86_64-unknown-linux-gnu
+
 cargo_check() {
  cargo check "$@"
  cargo clippy "$@" -- --deny=warnings
@@ -18,13 +30,12 @@ cargo_test() {
 
 cargo_test --features=alloc,experimental-derive,use-std,use-crc
 
-ensure_target thumbv7em-none-eabi
 cargo_check --target=thumbv7em-none-eabi --no-default-features
 cargo_check --target=thumbv7em-none-eabi --features=alloc,experimental-derive
 
 cargo fmt -- --check
 
-env RUSTDOCFLAGS='--cfg=docsrs --deny=warnings' cargo doc --no-deps --all-features
+env RUSTDOCFLAGS='--cfg=docsrs --deny=warnings' cargo +nightly doc --no-deps --all-features
 
 cd postcard-derive