Add missing source map for match-current-line

Currently `match-current-line` nodes don't have source map information. However Parser itself assumes that every node has source map information:

* `ruby-parse -L -e 'if /foo/; end'` crashes
    * https://github.com/whitequark/parser/blob/v2.1.2/lib/parser/runner/ruby_parse.rb#L32
* `Parser::Source::Comment.associate` with AST including `match-current-line` node crashes
    * https://github.com/whitequark/parser/blob/v2.1.2/lib/parser/source/comment/associator.rb#L106

This PR adds the missing source map information to `match-current-line` node.

On a related note, I've found [another source map missing node](https://github.com/whitequark/parser/blob/v2.1.2/lib/parser/builders/default.rb#L334) but I couldn't figure out how to handle it, so I left it.