Raise ModuleNotFound if a module is not found

While 026e0c1 did add the exception
class, it wasn't used. This avoids leaking an implementation detail.

Technically this is backwards incompatible, since it requires users to
change their code. It could make PuppetForge::ModuleNotFound inherit
from Faraday::ResourceNotFound, but that stil leaks the implementation
detail.

lib/puppet_forge/v3/module.rb

@@ -11,6 +11,11 @@ class Module < Base
       lazy :current_release, 'Release'
       lazy_collection :releases, 'Release'
 
+      def self.find(slug)
+        super
+      rescue Faraday::ResourceNotFound
+        raise PuppetForge::ModuleNotFound, "Module #{slug} not found"
+      end
     end
   end
 end

spec/unit/forge/v3/module_spec.rb

@@ -28,8 +28,8 @@
       expect(mod_stateless.name).to eq('apache')
     end
 
-    it 'returns nil for non-existent modules' do
-      expect { missing_mod }.to raise_error(Faraday::ResourceNotFound)
+    it 'raises exception for non-existent modules' do
+      expect { missing_mod }.to raise_error(PuppetForge::ModuleNotFound, 'Module absent-apache not found')
     end
   end