Fix issue with newer versions of language server and update LS depend…

…encies

Update LanguageServer to v4.5.1

Check for empty depot path string

Closes #24.

Emacs always passes a depot path to the julia script, but when it's an empty string that
indicates that the depot path elisp variable is not set. This will allow users to set their
own JULIA_DEPOT_PATH without having to configure eglot-jl.

Update julia packages

- Update versions of LanguageServer.jl and dependent packages for com…

…patibility with newer

  versions of julia

Changes from v2.1.1:

- Update to LanguageServer.jl v4.1.0 for compatibility with julia 1.7 (#28)

Bump version number

Merge pull request #16 from non-Jedi/ff/v2.1.0

v2.1.0

Version 2.0.0

Major version bump due to PR #9. The customizable variable
eglot-jl-default-environment has been removed. Instead eglot-jl will
use whatever environment is the default for Julia.

Clarify first-use instructions in README