Update elixir.yml

.github/workflows/elixir.yml

@@ -4,8 +4,8 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
-    - uses: actions/setup-elixir@v1.0.0
+    - uses: actions/checkout@v2
+    - uses: erlef/setup-elixir@v1
       with:
         otp-version: 22.x
         elixir-version: 1.9.x