x86_64-unknown-linux-gnu on ubuntu runner (#1975)

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
       uses: actions-rs/toolchain@v1
       with:
         toolchain: stable
-        target: aarch64-apple-darwin
+        target: x86_64-unknown-linux-gnu
         override: true
         components: rustfmt, clippy