feat: add pandoc to wordcount part (#32)

This simply adds the 'pandoc' filetype so the wordcount works with Vim-Pandoc and Vim-Pandoc-Syntax.

lua/hardline/parts/wordcount.lua

@@ -11,8 +11,9 @@ local options = {
     'markdown',
     'nroff',
     'org',
-    'rst',
+    'pandoc',
     'plaintex',
+    'rst',
     'tex',
     'text',
   },