Set require Moodle 3.8 and bump version higher than 3.7 branch.

version.php

@@ -23,9 +23,9 @@
  */
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version  = 2019072100;
+$plugin->version  = 2019072700;
-$plugin->requires = 2018102700; // Requires 3.6.
+$plugin->requires = 2019072500; // Requires 3.8.
-$plugin->release = '3.6.7';
+$plugin->release = '3.8.0';
 $plugin->maturity  = MATURITY_STABLE;
 $plugin->cron     = 0;
 $plugin->component = 'mod_attendance';