editors/tea: unbreak with hunspell 1.5

spellchecker.cpp:339:12: error: assigning to 'char *' from incompatible type 'const char *'

encoding = speller->get_dic_encoding();
         ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

PR: 214837
Approved by: portmgr blanket