Set the gravatar, so percy doesn't alert on every snapshot

spec/factories/member.rb

@@ -7,6 +7,7 @@ FactoryBot.define do
     confirmed_at { Time.zone.now }
     show_email { false }
     bio { 'I love seeds' }
+    preferred_avatar_uri { 'me.jpg'}
 
     # cropbot is needed for certain tests, eg. Crop.create_from_csv
     factory :cropbot do

spec/features/percy/percy_spec.rb

@@ -1,7 +1,8 @@
 require 'rails_helper'
 
 describe 'Test with visual testing', type: :feature, js: true do
-  let(:member) { FactoryBot.create :member, login_name: 'percy' }
+  let(:member) { FactoryBot.create :member, login_name: 'percy',
+    preferred_avatar_uri: 'http://www.gravatar.com/avatar/d021434aac03a7f7c7c0de60d07dad1c?size=150&default=identicon' }
   let!(:tomato) { FactoryBot.create :tomato }
   before do
     {