Add bash configuration

Sh is handled by bash tree-sitter parser.
`vim.treesitter.language.get_lang('sh')` returns `bash`.
This change makes this plugin work with both sh and bash files.

lua/ts_context_commentstring/config.lua

@@ -73,6 +73,7 @@ M.config = {
     rescript = { __default = '// %s', __multiline = '/* %s */' },
     scss = { __default = '// %s', __multiline = '/* %s */' },
     sh = '# %s',
+    bash = '# %s',
     solidity = { __default = '// %s', __multiline = '/* %s */' },
     sql = '-- %s',
     svelte = '<!-- %s -->',