gems: revert back to upstream solargraph now with rubocop 1.0 compat

See https://github.com/castwide/solargraph/issues/380 and previous commit e063b6cb4c

Gemfile

@@ -3,5 +3,3 @@
 source 'https://rubygems.org'
 
 gemspec
-
-gem 'solargraph', git: 'https://github.com/zaratan/solargraph.git', branch: 'fix_rubocop_1_0'

dyndnsd.gemspec

@@ -41,5 +41,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rake'
   s.add_development_dependency 'rspec'
   s.add_development_dependency 'rubocop', '~> 1.6.1'
-  # s.add_development_dependency 'solargraph', '~> 0.39.0'
+  s.add_development_dependency 'solargraph', '~> 0.40.0'
 end