Fix typo in comment

Author: sgerrand

.github/workflows/build.yml

@@ -48,7 +48,7 @@ jobs:
             os: ubuntu-latest
           - otp: 22.0
             elixir: 1.12.0
-            # It's necessary to run on ubunto 20.04 for OTP 20 - 25
+            # It's necessary to run on Ubuntu 20.04 for OTP 20 - 25
             # See https://github.com/erlef/setup-beam
             os: ubuntu-20.04       
     runs-on: ${{ matrix.version.os }}