Environment upgrades

Latest Ceedling
Ruby 2.7 + Alpine 3.11 (so we can get gcc 9)

Author: mkarlesky

Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:2.4.5-alpine3.8
+FROM ruby:2.7.1-alpine3.11
 
 MAINTAINER Michael Karlesky <[email protected]>
 
@@ -13,6 +13,12 @@ RUN apk --no-cache add \
 ##
 ## Copy assets for inclusion in image
 ##
+## Notes:
+## - Gems must be downloaded manually to the vendored assets/gems directory.
+## - To find the list of gems and versions needed, visit
+##     https://rubygems.org/gems/ceedling/versions/0.30.0/dependencies
+## - The easiest way to vendor a gem is `gem fetch <name> -v <version>` in assets/gems.
+##
 
 COPY assets/gems /assets/gems