Handle not found errors

Return `nil` when a repository is not found rather than raise an octokit error

Signed-off-by: Justin Kenyon <[email protected]>

Author: kenyonj

test/test_helper.rb

@@ -88,6 +88,8 @@ def repository(item)
   rescue Octokit::TooManyRequests
     repos[:skip_requests] = true
     repos[item] = true
+  rescue Octokit::NotFound
+    repos[item] = nil
   end
 
   def user(item)