fix rescuing LoadError rather than HttpError.

This changes what errors are raised.  If brewerydb returns any status value that is not a 200
then an HttpError is raised, this should be handled by the application that is using tankard.

Load error can be thrown if MultiJson runs into parsing issues with the data returned.

lib/tankard/api/beer.rb

@@ -85,7 +85,7 @@ def find_on_single_page(block)
         def request_data_with_nil_on_error(uri, options)
           begin
             @request.get(uri, options)["data"]
-          rescue Tankard::Error::HttpError
+          rescue Tankard::Error::LoadError
             nil
           end
         end

lib/tankard/api/beers.rb

@@ -67,7 +67,7 @@ def request_data_with_nil_on_error(uri, options)
         def request_with_nil_on_error(uri, options)
           begin
             @request.get(uri, options)
-          rescue Tankard::Error::HttpError
+          rescue Tankard::Error::LoadError
             nil
           end
         end