Lock rubocop-ast to < 0.7

The latest versions of rubocop-ast (>= 0.7) are incompatible with older versions of rubocop. Since grape currently use rubocop 0.84 we need to lock rubocop-ast to a compatible version

Author: Tim Connor

Gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/multi_json.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/multi_xml.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/rack1.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/rack2.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/rack_edge.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/rails_5.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/rails_6.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end
 

gemfiles/rails_edge.gemfile

@@ -11,6 +11,7 @@ group :development, :test do
   gem 'hashie'
   gem 'rake'
   gem 'rubocop', '0.84.0'
+  gem 'rubocop-ast', '< 0.7'
   gem 'rubocop-performance', require: false
 end