Update check-cfg flag (#135)

Reflects the updates in Cargo nightly: rust-lang/cargo#12845

Author: illicitonion

.github/workflows/features.yml

@@ -22,5 +22,5 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: check
-          args: -Z unstable-options -Z check-cfg=features --tests
+          args: -Z unstable-options -Z check-cfg --tests
           toolchain: nightly