current directory:
/home/travis/.rvm/gems/ruby-1.9.3-p551/gems/ffi-1.11.0/ext/ffi_c
/home/travis/.rvm/rubies/ruby-1.9.3-p551/bin/ruby -r
./siteconf20190519-6015-12z6hsq.rb extconf.rb
checking for ffi_call() in -lffi... yes
checking for ffi_closure_alloc()... yes
checking for shlwapi.h... no
checking for rb_thread_call_without_gvl()... yes
checking for ruby_native_thread_p()... yes
checking for ruby_thread_has_gvl_p()... no
checking for ffi_prep_cif_var()... yes
checking for ffi_raw_call()... yes
checking for ffi_prep_raw_closure()... yes
creating extconf.h
creating Makefile
current directory:
/home/travis/.rvm/gems/ruby-1.9.3-p551/gems/ffi-1.11.0/ext/ffi_c
make  clean
current directory:
/home/travis/.rvm/gems/ruby-1.9.3-p551/gems/ffi-1.11.0/ext/ffi_c
make
compiling Call.c
Call.c:46:25: fatal error: ruby/thread.h: No such file or directory
 #include <ruby/thread.h>
                         ^
compilation terminated.
make: *** [Call.o] Error 1
make failed, exit code 2
Gem files will remain installed in
/home/travis/.rvm/gems/ruby-1.9.3-p551/gems/ffi-1.11.0 for inspection.
Results logged to
/home/travis/.rvm/gems/ruby-1.9.3-p551/extensions/x86_64-linux/1.9.1/ffi-1.11.0/gem_make.out
An error occurred while installing ffi (1.11.0), and Bundler cannot
continue.
Make sure that `gem install ffi -v '1.11.0' --source 'https://rubygems.org/'`
succeeds before bundling.
In ruby_19.gemfile:
  aruba was resolved to 0.14.9, which depends on
    ffi