[rubygems/rubygems] Lock rubocop version to 0.80.1

The later RuboCop versions don't work with ruby2.3
so we should lock the version to what works with
ruby2.3 as we haven't dropped the support yet.

And since we're using the older version of rubocop,
also fix `Max` value of `LineLength` to 120, which
is the current standard. Without this, rubocop
will throw the line length offenses.

Signed-off-by: Utkarsh Gupta <utkarsh@debian.org>

https://github.com/rubygems/rubygems/commit/46d0a800a2

lib/bundler/templates/newgem/rubocop.yml.tt

@@ -5,3 +5,6 @@ Style/StringLiterals:
 Style/StringLiteralsInInterpolation:
   Enabled: true
   EnforcedStyle: double_quotes
+
+Layout/LineLength:
+  Max: 120

spec/bundler/commands/newgem_spec.rb

@@ -177,7 +177,7 @@ RSpec.describe "bundle gem" do
 
     it "run rubocop inside the generated gem with no offenses" do
       prepare_gemspec(bundled_app(gem_name, "#{gem_name}.gemspec"))
-      gems = ["rake", "rubocop"]
+      gems = ["rake", "rubocop -v 0.80.1"]
       path = Bundler.feature_flag.default_install_uses_path? ? local_gem_path(:base => bundled_app(gem_name)) : system_gem_path
       realworld_system_gems gems, :path => path
       bundle "exec rubocop --ignore-parent-exclusion", :dir => bundled_app(gem_name)