Try to switch WASI CI to nightly

Author: RReverser

azure-pipelines.yml

@@ -36,6 +36,8 @@ jobs:
     - script: rustup target add wasm32-unknown-unknown
     - script: cargo build --target wasm32-unknown-unknown
 - job: wasi
+  parameters:
+    toolchain: nightly
   steps:
     - template: ci/azure-install-rust.yml
     - script: rustup target add wasm32-unknown-wasi