Use rust nightly for Github actions build

.github/workflows/rust.yml

@@ -8,7 +8,11 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
+    - uses: actions-rs/toolchain@v1
+      with:
+        profile: minimal
+        toolchain: nightly
     - name: Install dependencies
       run: sudo apt-get update && sudo apt-get install libsdl2-dev
     - name: Build

rust-toolchain

@@ -0,0 +1 @@
+nightly