Install ruby failed on el capitan
El Capitan 上用brew 安装ruby的时候，碰到此错误
```
brew install rbenv ruby-build
rbenv install 2.2.2
will failed with this error,
Results logged to /var/folders/ys/0h6glx5s3gj00zv0p6w3rhy00000gn/T/ruby-build.20150904110309.45724.log
Last 10 log lines:
The Ruby openssl extension was not compiled.
ERROR: Ruby install aborted due to missing extensions
Configure options used:
--prefix=/Users/dfang/.rbenv/versions/2.2.3
--with-readline-dir=/usr/local/opt/readline
--with-openssl-dir=/usr/local/opt/openssl
CC=clang
CFLAGS= -O3 -Wno-error=shorten-64-to-32
LDFLAGS=-L/Users/dfang/.rbenv/versions/2.2.3/lib
CPPFLAGS=-I/Users/dfang/.rbenv/versions/2.2.3/include
```
CONFIGURE_OPTS="--with-readline-dir=$(brew --prefix readline) --with-openssl-dir=$(brew --prefix openssl)" rbenv install -k -v 2.2.2 does not work.
you just need to link openssl brew link --force openssl
and also it's better to install ruby build this way instead of brew install ruby-build
git clone https://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build
https://ruby-china.org/topics/16073
