Revert "bundler-audit 0.7.0"

This mostly reverts b1d02e7, adding a
>= 0.7.0 to ensure we can use Thor 2 as described in that commit.

Without this commit this generator creates a broken Gemfile because the
0.7.0 no longer exists.

lib/suspenders/generators/advisories_generator.rb

@@ -3,11 +3,7 @@
 module Suspenders
   class AdvisoriesGenerator < Generators::Base
     def bundler_audit_gem
-      gem "bundler-audit",
-          require: false,
-          group: %i[development test],
-          git: "https://github.com/rubysec/bundler-audit.git",
-          branch: "0.7.0"
+      gem "bundler-audit", ">= 0.7.0", require: false, group: %i[development test]
       Bundler.with_clean_env { run "bundle install" }
     end