Update elixir.yml

Author: fahchen

.github/workflows/elixir.yml

@@ -27,7 +27,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Setup elixir
-      uses: erlef/setup-beam@v1
+      uses: erlef/setup-elixir@v1
       with:
         elixir-version: 1.9.4 # Define the elixir version [required]
         otp-version: 22.2 # Define the OTP version [required]