gron.nanorc: improve *_COLORS variable value highlight

Author: mattirn

demo/src/main/scripts/nanorc/gron.nanorc

@@ -5,7 +5,8 @@ NUMBER:     "\<[-]?[0-9]*([Ee][+-]?[0-9]+)?\>"  "\<[-]?[0](\.[0-9]+)?\>"
 STRING:     "[a-zA-Z]+[a-zA-Z0-9]*"
 NULL:       "\<null\>"
 BOOLEAN:    "\<(true|false)\>"
-VARIABLE:   "(\[|,)\s*[a-zA-Z0-9]*\s*:"
-PLAIN:      "(:|\[|,|\])"
+VARIABLE:   "(\[|,)\s*[a-zA-Z0-9_]*\s*:"
+VARIABLE:   "(^|:)[a-zA-Z0-9_]*="
+PLAIN:      "(=|:|\[|,|\])"
 ESCAPE:     "\\u[0-9a-fA-F]{4}|\\[bfnrt'"/\\]"
 $BALANCED_DELIMITERS  "", '"