Make the update plugin script take an optional argument

If an argument is given, it will grep the list of plugins for it and
update the first match rather then the first available for an update

bin/updatePlugin

@@ -1,5 +1,9 @@
 #!/usr/bin/sh
-plugin=$(wp plugin list 2> /dev/null | grep available | head -n 1 | awk '{print $1}')
+if [ -n "$1" ]; then
+	plugin=$(wp plugin list 2> /dev/null | grep available | grep $1 | head -n 1 | awk '{print $1}')
+else
+	plugin=$(wp plugin list 2> /dev/null | grep available | head -n 1 | awk '{print $1}')
+fi
 echo "$plugin"
 versions=$(wp plugin update $plugin 2> /dev/null | tail -n 2 | head -n 1 | awk '{print $2 "->" $3}')
 echo "$versions"