Use ruby-2.7.4 (#16481)

Stop using older version of resolv gem as the bug has been fixed.
https://bugs.ruby-lang.org/issues/17781

.ruby-version

@@ -1 +1 @@
-2.7.2
+2.7.4

Dockerfile

@@ -26,7 +26,7 @@ RUN ARCH= && \
 	mv node-v$NODE_VER-linux-$ARCH /opt/node
 
 # Install Ruby
-ENV RUBY_VER="2.7.2"
+ENV RUBY_VER="2.7.4"
 RUN apt-get update && \
   apt-get install -y --no-install-recommends build-essential \
     bison libyaml-dev libgdbm-dev libreadline-dev libjemalloc-dev \

Gemfile

@@ -155,5 +155,3 @@ gem 'concurrent-ruby', require: false
 gem 'connection_pool', require: false
 
 gem 'xorcist', '~> 1.1'
-
-gem 'resolv', '~> 0.1.0'

Gemfile.lock

@@ -491,7 +491,6 @@ GEM
     regexp_parser (2.1.1)
     request_store (1.5.0)
       rack (>= 1.4)
-    resolv (0.1.0)
     responders (3.0.1)
       actionpack (>= 5.0)
       railties (>= 5.0)
@@ -764,7 +763,6 @@ DEPENDENCIES
   rdf-normalize (~> 0.4)
   redis (~> 4.3)
   redis-namespace (~> 1.8)
-  resolv (~> 0.1.0)
   rqrcode (~> 2.0)
   rspec-rails (~> 5.0)
   rspec-sidekiq (~> 3.1)