Fix elixir version in publish action

Author: athal7

.github/workflows/publish.yml

@@ -6,7 +6,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     container:
-      image: elixir:1.9.1-slim
+      image: elixir:1.10.4-slim
     steps:
     - uses: actions/checkout@v2.3.4
     - name: Install Dependencies