use ubuntu-latest for workflows

Author: the-mikedavis

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ on: push
 jobs:
   bless:
     name: Bless
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-latest
     env:
       MIX_ENV: test
       ECHO_HOST: localhost
@@ -89,7 +89,7 @@ jobs:
 
   publish-hex-package:
     name: Publish Hex Package ⬆️☁️
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-latest
     if: startsWith(github.ref, 'refs/tags/v')
     env:
       MIX_ENV: dev

.github/workflows/refresh-dev-cache.yml

@@ -31,7 +31,7 @@ env:
 jobs:
   refresh-dev-cache:
     name: Refresh Docs Cache
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-latest
     env:
       MIX_ENV: dev