Fix failing sanity check spec under latest bundler (rspec#1912)

Relax the regexp for matching the expected "uninitialized constant"
error to fix this spec failure when running on Bundler 1.16.0 and Ruby
2.4.2:

expected "NameError: uninitialized constant RSpec::Support"
to match /uninitialized constant RSpec::Support \(NameError\)/

Author: mattbrictson

spec/sanity_check_spec.rb

@@ -19,7 +19,7 @@
 
     Bundler.with_clean_env do
       expect(`bundle exec #{script} 2>&1`).
-        to match(/uninitialized constant RSpec::Support \(NameError\)/).
+        to match(/uninitialized constant RSpec::Support/).
         or match(/undefined method `require_rspec_core' for RSpec::Support:Module/)
 
       expect($?.exitstatus).to eq(1)