Ruby 2.6 isn't really supported

[alagos]

According to the gemspec it is, but in practice I'm getting:

ERROR:  Error installing solargraph:
	There are no versions of rubocop-ast (>= 1.31.1, < 2.0) compatible with your Ruby & RubyGems. Maybe try installing an older version of the gem you're looking for?
	rubocop-ast requires Ruby version >= 2.7.0. The current ruby version is 2.6.10.210.

I tried installing rubocop 1.50.2 as 1.51.0 dropped the 2.6 support and that worked. So it should be dropped ruby 2.6 support or added to the gemspec:

s.add_runtime_dependency 'rubocop', '~> 1.50.0'