Adds upgrade routine

mailchimp_upgrade.php

@@ -0,0 +1,38 @@
+<?php
+/**
+ * Upgrade routines.
+ *
+ * @package Mailchimp
+ */
+
+/**
+ * Check plugin version.
+ *
+ * @since 1.6.0
+ * @return void
+ */
+function mailchimp_version_check() {
+	$db_option = get_option( 'mc_version' );
+
+	if ( MCSF_VER === $db_option ) {
+		return;
+	}
+
+	if ( false === $db_option || version_compare( '1.6.0', $db_option, '>' ) ) {
+		mailchimp_update_1_6_0();
+	}
+
+	update_option( 'mc_version', MCSF_VER );
+}
+
+add_action( 'plugins_loaded', 'mailchimp_version_check' );
+
+/**
+ * Version 1.6.0 update routine
+ *   - Remove MonkeyRewards checkbox option
+ *
+ * @return void
+ */
+function mailchimp_update_1_6_0() {
+	delete_option( 'mc_rewards' );
+}