Remove Rspec convention in favour of solargraph-rspec plugin

[lekemula]

Hi,

ICYMI: #683 (comment)

The new plugin includes all existing functionality + much more! (See gem's README: https://github.com/lekemula/solargraph-rspec.)

After you have given it a try and find it worthy, being that rspec is the de-facto preferred testing framework in Ruby, would it make sense to:

• mention it alongside solargraph-rails in the Readme/Documentation?
• remove the exclude: ['spec/**/*'] folder as a default config?
  

  solargraph/lib/solargraph/workspace/config.rb

  Line 151 in d610a6b

  'exclude' => ['spec/**/*', 'test/**/*', 'vendor/**/*', '.bundle/**/*'],

Looking forward to your feedback.

Resolves: #683

[lekemula]

remove the exclude: ['spec/**/*'] folder as a default config?

@castwide It turns out that keeping the specs folder in the exclude list, is a good idea. Luckily Solargraph still parses them when opened or changed in the editor, something which I initially thought was a bug, but in our case, it's a very important feature allowing us to "lazy parse" specs 🥳

lekemula/solargraph-rspec@3f0fc39

It's worth mentioning that with this setup, there was no performance issues or degradation whatsoever when testing against Gitlab's codebase.