Fix using most recent versions of the Ruby images in the CI

Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:2.7.1
+FROM ruby:2.7
 
 # throw errors if Gemfile has been modified since Gemfile.lock
 RUN bundle config --global frozen 1

Dockerfile-2.5

@@ -1,4 +1,4 @@
-FROM ruby:2.5.7
+FROM ruby:2.5
 
 # throw errors if Gemfile has been modified since Gemfile.lock
 RUN bundle config --global frozen 1

Dockerfile-2.6

@@ -1,4 +1,4 @@
-FROM ruby:2.6.5
+FROM ruby:2.6
 
 # throw errors if Gemfile has been modified since Gemfile.lock
 RUN bundle config --global frozen 1

script/poll-for-db

@@ -4,7 +4,7 @@ appdir=$(cd $(dirname "$0")/.. && pwd)
 [ -f /etc/app-env ] || exec "$appdir/script/docker-environment" $0 $@
 
 for i in {1..60}; do
-  curl -sf db:3306 >/dev/null && exit
+  curl -sf telnet://db:3306 >/dev/null && exit
   sleep 1
 done