add keys and certs made by mk_simple_certs.py to .gitignore
add keys and certs made by mk_simple_certs.py to .gitignore

aalba6675/pyopenssl,sholsapp/pyopenssl,pyca/pyopenssl,kjav/pyopenssl,mschmo/pyopenssl,mhils/pyopenssl,samv/pyopenssl,hynek/pyopenssl,sorenh/pyopenssl,daodaoliang/pyopenssl,hynek/pyopenssl,reaperhulk/pyopenssl,reaperhulk/pyopenssl,mitghi/pyopenssl,r0ro/pyopenssl,adamwolf/pyopenssl,mhils/pyopenssl,mitghi/pyopenssl,aalba6675/pyopenssl,r0ro/pyopenssl