Bump lint job to latest Elixir/Erlang version (#31)

Author: kianmeng

.github/workflows/ci.yml

@@ -19,8 +19,8 @@ jobs:
               elixir: 1.7.4
               otp: 20.3.8.26
           - pair:
-              elixir: 1.11.4
-              otp: 23.2.7
+              elixir: 1.13.4
+              otp: 25.0.4
             lint: lint
     steps:
       - uses: actions/checkout@v2