diff --git a/Dockerfile b/Dockerfile
index 2b6ddd3..b1e36b4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:2.4.5-alpine3.8
+FROM ruby:2.7.1-alpine3.11
 
 MAINTAINER Michael Karlesky <michael@karlesky.net>
 
@@ -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
 
diff --git a/assets/gems/ceedling-0.29.1.gem b/assets/gems/ceedling-0.29.1.gem
deleted file mode 100644
index 603798b..0000000
Binary files a/assets/gems/ceedling-0.29.1.gem and /dev/null differ
diff --git a/assets/gems/ceedling-0.30.0.gem b/assets/gems/ceedling-0.30.0.gem
new file mode 100644
index 0000000..092803e
Binary files /dev/null and b/assets/gems/ceedling-0.30.0.gem differ
diff --git a/assets/gems/thor-0.20.3.gem b/assets/gems/thor-0.20.3.gem
deleted file mode 100644
index 9a88db7..0000000
Binary files a/assets/gems/thor-0.20.3.gem and /dev/null differ
diff --git a/assets/gems/thor-1.0.1.gem b/assets/gems/thor-1.0.1.gem
new file mode 100644
index 0000000..d7d0a79
Binary files /dev/null and b/assets/gems/thor-1.0.1.gem differ