Get gitlab-shell verion from file for install rake task

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

lib/tasks/gitlab/shell.rake

@@ -4,7 +4,8 @@ namespace :gitlab do
     task :install, [:tag, :repo] => :environment do |t, args|
       warn_user_is_not_gitlab
 
-      args.with_defaults(tag: "v1.9.3", repo: "https://gitlab.com/gitlab-org/gitlab-shell.git")
+      default_version = File.read(File.join(Rails.root, "GITLAB_SHELL_VERSION")).strip
+      args.with_defaults(tag: default_version, repo: "https://gitlab.com/gitlab-org/gitlab-shell.git")
 
       user = Settings.gitlab.user
       home_dir = Settings.gitlab.user_home