Update solr_http_retry.go
Update solr_http_retry.go

Replaced fmt.Errorf with errors.New, the latter being over 3 times faster than the former in my testing.  
Also removed `&& err == nil`, as to have reached that conditional, err has to be nil anyways so that singular expression evaluates to true every time anyways. Do correct me if im wrong
sendgrid/go-solr,sendgrid/go-solr,sendgrid/go-solr