textproc/enchant: unbreak with hunspell 1.5

myspell_checker.cpp:430:8: error: cannot initialize a variable of type 'char *' with an rvalue of

type 'const char *'
  char *enc = myspell->get_dic_encoding();
        ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~

https://github.com/hunspell/hunspell/commit/971f8a9cf52e

PR: 214837
Approved by: portmgr blanket