default gems are not found by bundler #376
Description
e.g. in case of json 1.8.3 bundled with jruby 9.1.0.0 (from jruby/jruby#3850) :
Could not find json-1.8.3-java in any of the sources
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/spec_set.rb:95:in `block in materialize'
from org/jruby/RubyArray.java:2332:in `map!'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/spec_set.rb:88:in `materialize'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/definition.rb:140:in `specs'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/definition.rb:185:in `specs_for'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/definition.rb:174:in `requested_specs'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/environment.rb:19:in `requested_specs'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/runtime.rb:14:in `setup'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler.rb:95:in `setup'
from /var/lib/tomcat6/webapps/secure/WEB-INF/gems/gems/bundler-1.12.1/lib/bundler/setup.rb:19:in `<top>'
from org/jruby/RubyKernel.java:937:in `require'
from uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:1:in `(root)'
from uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:128:in `<top>'
from org/jruby/RubyKernel.java:937:in `require'
from /var/lib/tomcat6/webapps/secure/WEB-INF/config/boot.rb:6:in `(root)'
from uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:1:in `(root)'
from uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:54:in `require'
from uri:classloader:/jruby/rack/rails/environment3.rb:23:in `<top>'