gem install json -v '1.8.1'
Building native extensions.  This could take a while...
ERROR:  Error installing json:
	ERROR: Failed to build gem native extension.

    current directory: /home/captain/.rvm/gems/ruby-2.3.0/gems/json-1.8.1/ext/json/ext/generator
/home/captain/.rvm/rubies/ruby-2.3.0/bin/ruby -r ./siteconf20170414-19840-77dayi.rb extconf.rb
creating Makefile

current directory: /home/captain/.rvm/gems/ruby-2.3.0/gems/json-1.8.1/ext/json/ext/generator
make "DESTDIR=" clean

current directory: /home/captain/.rvm/gems/ruby-2.3.0/gems/json-1.8.1/ext/json/ext/generator
make "DESTDIR="
compiling generator.c
In file included from generator.c:1:0:
../fbuffer/fbuffer.h: In function ‘fbuffer_to_s’:
../fbuffer/fbuffer.h:175:47: error: macro "rb_str_new" requires 2 arguments, but only 1 given
../fbuffer/fbuffer.h:175:20: warning: initialization makes integer from pointer without a cast [enabled by default]
Makefile:238: recipe for target 'generator.o' failed
make: *** [generator.o] Error 1

make failed, exit code 2

Gem files will remain installed in /home/captain/.rvm/gems/ruby-2.3.0/gems/json-1.8.1 for inspection.
Results logged to /home/captain/.rvm/gems/ruby-2.3.0/extensions/x86_64-linux/2.3.0/json-1.8.1/gem_make.out