Bump .solargraph.yml.example max files

What does this MR do and why?

Locally, my solargraph said there were 15034 files. So the max files should be set to something higher.

As an example I attempted to get the number of files. This command is not exactly correct, since it includes e.g. directory paths like ./qa/qa/specs/features which are not .rb files, but it's good enough to show that 15000 is no longer an appropriate max_files setting:

➜  gitlab git:(master) find . \( -name 'spec' -o -path ./vendor -o -path ./.bundle -o -path ./qa/qa/specs/features \) -prune -o -name '*.rb' | wc -l  
   15050

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