cleanup so gravatar download failures are consistent

previously we would ignore socket error, but this would mean that
there could be conditions where we would keep trying to download
gravatars forever (in an hourly job)

spec/models/user_avatar_spec.rb

@@ -74,7 +74,9 @@ describe UserAvatar do
 
         FileHelper.expects(:download).raises(SocketError)
 
-        expect { avatar.update_gravatar! }.to_not change { Upload.count }
+        expect do
+          expect { avatar.update_gravatar! }.to raise_error(SocketError)
+        end.to_not change { Upload.count }
 
         expect(avatar.last_gravatar_download_attempt).to eq(Time.now)
       end