bundle installでずっとエラーが出ているのですが
どのように解決したらいいかわかる方いらっしゃいますでしょうか。

Fetching gem metadata from https://rubygems.org/...........
Fetching version metadata from https://rubygems.org/...
Fetching dependency metadata from https://rubygems.org/..
Using rake 10.4.2
Using i18n 0.7.0
Installing json 1.8.3 with native extensions

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

/Users/user/.rbenv/versions/2.1.5/bin/ruby extconf.rb

/Users/user/.rbenv/versions/2.1.5/bin/ruby: invalid option -1 (-h will show valid options) (RuntimeError)

extconf failed, exit code 1

Gem files will remain installed in /Users/user/.Trash/first_app 14.39.04/rails-application-build-guide-sample/form/bulk_registration_form_example/vendor/bundle/ruby/2.1.0/gems/json-1.8.3 for inspection.
Results logged to /Users/user/.Trash/first_app 14.39.04/rails-application-build-guide-sample/form/bulk_registration_form_example/vendor/bundle/ruby/2.1.0/extensions/x86_64-darwin-14/2.1.0-static/json-1.8.3/gem_make.out
An error occurred while installing json (1.8.3), and Bundler cannot continue.
Make sure that gem install json -v '1.8.3' succeeds before bundling.