~cdrozak/tree-sitter-tcl#17: Variables with underscores are interpreted as concatenation

For example:

puts $auto_path

gets interpreted as:

(command
 name: (word)
 arguments: (word_list
             (concatenation
              (variable_substitution)
              (word))))

instead of:

(command
 name: (word)
 arguments: (word_list
             (variable_substitution)))