[rubygems/rubygems] Make sure RSpec diffs don't omit the different part

We sometimes check assertions on lockfile contents, which involves
comparing a reasonably long string. Sometimes RSpec is not able to show
the part of the string that's actually different, making it hard to
figure out the issue.

Configuring this setting should fix the issue in most cases.

https://github.com/rubygems/rubygems/commit/5ad8ee499e

spec/bundler/spec_helper.rb

@@ -58,6 +58,8 @@ RSpec.configure do |config|
 
   config.expect_with :rspec do |c|
     c.syntax = :expect
+
+    c.max_formatted_output_length = 1000
   end
 
   config.mock_with :rspec do |mocks|