fix(sources.treesitter): ts source not returning symbols (#189)

Bug:    Treesitter source does not return any symbols.
Fix:    Remove use of deprecated `opts.sources.treesitter.name_pattern`
	which is always nil. Use `opts.sources.treesitter.name_regex` to
	get name for the treesitter node.

lua/dropbar/sources/treesitter.lua

@@ -21,7 +21,7 @@ local function get_node_short_name(node, buf)
     .trim(
       vim.fn.matchstr(
         vim.treesitter.get_node_text(node, buf):gsub('\n', ' '),
-        configs.opts.sources.treesitter.name_pattern
+        configs.opts.sources.treesitter.name_regex
       )
     )
     :gsub('%s+', ' ')