Change if-statement for private keys to more portable version

acme.sh

@@ -1003,7 +1003,7 @@ _sign() {
 
   _sign_openssl="${ACME_OPENSSL_BIN:-openssl} dgst -sign $keyfile "
 
-  if egrep -o "BEGIN( RSA)? PRIVATE KEY" "$keyfile" >/dev/null 2>&1; then
+  if grep "BEGIN RSA PRIVATE KEY" "$keyfile" >/dev/null 2>&1; || if grep "BEGIN PRIVATE KEY" "$keyfile" >/dev/null 2>&1;
     $_sign_openssl -$alg | _base64
   elif grep "BEGIN EC PRIVATE KEY" "$keyfile" >/dev/null 2>&1; then
     if ! _signedECText="$($_sign_openssl -sha$__ECC_KEY_LEN | ${ACME_OPENSSL_BIN:-openssl} asn1parse -inform DER)"; then