Try to load after other plugins in case of custom taxonomies

If using the default priority (10) plugins whose name starts with a letter
after "r"  will load after "radio buttons for taxonomies" therefor function 
"launch" won't recognize or find custom taxonomies with taxonomy_exists()
Fixed "Undefined variable: taxonomy" error

Error message in custom tax columns:
Notice: Undefined variable: taxonomy in /wp-content/plugins/Radio-Buttons-for-Taxonomies/inc/class.WordPress_Radio_Taxonomy.php on line 452