Upgrade Ruby to version 2.7.4

Note this version includes Bundler 2, so we can finally upgrade.

.gitlab-ci.yml

@@ -3,7 +3,7 @@ stages:
   - lint
 
 tests:
-  image: "ruby:2.6.8"
+  image: "ruby:2.7.4"
   stage: test
   services:
     - postgres:10.10
@@ -34,7 +34,7 @@ tests:
 # PRONTO_GITLAB_API_PRIVATE_TOKEN to your repository CI/CD settings
 # giving it the value of the Personal Access Token
 linters:
-  image: "ruby:2.6.8"
+  image: "ruby:2.7.4"
   stage: lint
   cache:
     key: consul

.ruby-version

@@ -1 +1 @@
-2.6.8
+2.7.4

Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:2.6.8-buster
+FROM ruby:2.7.4-buster
 
 ENV DEBIAN_FRONTEND noninteractive
 

Gemfile.lock

@@ -795,4 +795,4 @@ DEPENDENCIES
   wkhtmltopdf-binary (~> 0.12.6)
 
 BUNDLED WITH
-   1.17.2
+   2.1.4

README.md

@@ -38,7 +38,7 @@ You can access the main website of the project at [http://consulproject.org](htt
 
 **NOTE**: For more detailed instructions check the [docs](https://docs.consulproject.org)
 
-Prerequisites: install git, Ruby 2.6.8, CMake, pkg-config, shared-mime-info, Node.js and PostgreSQL (>=9.5).
+Prerequisites: install git, Ruby 2.7.4, CMake, pkg-config, shared-mime-info, Node.js and PostgreSQL (>=9.5).
 
 ```bash
 git clone https://github.com/consul/consul.git

README_ES.md

@@ -36,7 +36,7 @@ Puedes acceder a la página principal del proyecto en [http://consulproject.org]
 
 **NOTA**: para unas instrucciones más detalladas consulta la [documentación](https://docs.consulproject.org)
 
-Prerequisitos: tener instalado git, Ruby 2.6.8, CMake, pkg-config, shared-mime-info, Node.js y PostgreSQL (9.5 o superior).
+Prerequisitos: tener instalado git, Ruby 2.7.4, CMake, pkg-config, shared-mime-info, Node.js y PostgreSQL (9.5 o superior).
 
 ```bash
 git clone https://github.com/consul/consul.git