Update the language server to 0.13.0

[rcjsuen]

This update includes a small linting fix as well as highlighting support for heredocs. You can use the file below to test the changes.

1. The :- syntax provides a default so we should not be flagging the FROM as an error (see Evaluate variable default values in determining if blank rcjsuen/dockerfile-language-server#269).
2. The language server now provides proper support for the start and end of a heredoc by highlighting the two ends and allowing you to jump from the end of the document to the original definition at the top.

# the FROM line should no longer be flagged as an error
FROM ${VAR:-alpine}

# 1. clicking on "file" on lines 6 or 8 should highlight the two occurrences
# 2. you can now use "Go to Definition" on line 8 to jump to line 6
RUN echo <<file
abc
file