Update server_configurations.md

[adigitoleo]

Update links for fortls

[github-actions[bot]]

Note that server_configurations.md or server_configurations.txt will be regenerated by the docgen CI process. Edit the Lua source file instead. For details on generating documentation, see: https://github.com/neovim/nvim-lspconfig/blob/master/CONTRIBUTING.md#generating-docs

[github-actions[bot]]

Note that server_configurations.md or server_configurations.txt will be regenerated by the docgen CI process. Edit the Lua source file instead. For details on generating documentation, see: https://github.com/neovim/nvim-lspconfig/blob/master/CONTRIBUTING.md#generating-docs