Add rpm-spec-language-server to Implementations.md

[dcermak]

Description

Add rpm-spec-language-server to Implementations.md

Code review checklist (for code reviewer to complete)

• [x] Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• [x] Title summarizes what is changing
• [x] Commit messages are meaningful (see [this][commit messages] for details)
• [x] Tests have been included and/or updated, as appropriate
• [x] Docstrings have been included and/or updated, as appropriate
• [x] Standalone docs have been updated accordingly

[tombh]

Just need to update the commit message to docs: rpm-spec-language-server to Implementations.md

[tombh]

Thank you ✨