Replace egrep with grep -E

This is an alternative to the proposed patch in #154 and is easier to
read than the change.

Closes #154.

Signed-off-by: Eric F Crist <ecrist@secure-computing.net>

ChangeLog

@@ -1,5 +1,9 @@
 Easy-RSA 3 ChangeLog
 
+3.0.4 (TBD)
+    * Remove use of egrep (#154)
+
+
 3.0.3 (2017-08-22)
     * Include mktemp windows binary
     * copy CSR extensions into signed certificate

easyrsa3/easyrsa

@@ -942,7 +942,7 @@ default_server_san() {
 		"$EASYRSA_OPENSSL" req -in "$path" -noout -subject -nameopt sep_multiline |
 		awk -F'=' '/^  *CN=/{print $2}'
 		)
-	echo "$cn" | egrep -q '^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$'
+	echo "$cn" | grep -E -q '^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$'
 	if [ $? -eq 0 ]; then
 		print "subjectAltName = IP:$cn"
 	else