[staging] Remove vendor cache from staging gem

They are not big (compared with spec), but they aren't useful to
rubygems.
  This change doesn't bump the gem version to minimize impact
on other more important in-flight changes on staging.

Change-Id: If5b299823378a85e7bd98f517ee36f6b302602a7

staging/vcap_staging.gemspec

@@ -24,5 +24,5 @@ gemspec = Gem::Specification.new do |s|
   s.bindir       = 'bin'
   s.require_path = 'lib'
 
-  s.files        = %w(Rakefile) + Dir.glob("{lib,vendor}/**/*")
+  s.files        = %w(Rakefile) + Dir.glob("lib/**/*")
 end