Use stable

Author: termoshtt

.github/workflows/rust.yml

@@ -33,7 +33,7 @@ jobs:
       - uses: actions/checkout@v2
       - name: Generate code coverage
         run: |
-          cargo +nightly tarpaulin --verbose --features=intel-mkl --workspace --timeout 120 --out Xml
+          cargo tarpaulin --verbose --features=intel-mkl --workspace --timeout 120 --out Xml
       - name: Upload to codecov.io
         uses: codecov/codecov-action@v1
         with: