run clippy, docs and fmt checks on stable

I think this ran on nightly because clippy needed that. I'm pretty sure clippy runs fine on stable now.

Author: mendelt

.github/workflows/ci.yaml

@@ -76,11 +76,6 @@ jobs:
     steps:
     - uses: actions/checkout@master
 
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: nightly
-        override: true
-
     - name: setup
       run: |
         rustup component add clippy rustfmt