update nightly (#510)

Author: xlc

.github/workflows/test.yml

@@ -19,7 +19,7 @@ jobs:
       uses: actions-rs/toolchain@v1
       with:
         profile: minimal
-        toolchain: nightly-2021-03-01
+        toolchain: nightly-2021-03-15
         components: rustfmt
         target: wasm32-unknown-unknown
         override: true