fix gem trouble for high sierra

log.sh

$ gem install aws-sdk
Fetching: jmespath-1.3.1.gem (100%)
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.3.0 directory.
$ which ruby
/usr/bin/ruby
$ which gem
/usr/bin/gem
$ brew install rbenv ruby-build
$ rbenv install --list
$ touch ~/.bash_profile
# add following line to ~/.bash_profile
# eval "$(rbenv init -)"
$ rbenv install 2.3.0
$ ownloading ruby-2.3.0.tar.bz2...
-> https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.0.tar.bz2
Installing ruby-2.3.0...

BUILD FAILED (OS X 10.13 using ruby-build 20160130)

Inspect or clean up the working tree at /var/folders/ld/gp_hcv8d66v689s__kk689gw0000gr/T/ruby-build.20171023153742.76600
Results logged to /var/folders/ld/gp_hcv8d66v689s__kk689gw0000gr/T/ruby-build.20171023153742.76600.log

Last 10 log lines:
installing capi-docs:         /Users/omiya/.rbenv/versions/2.3.0/share/doc/ruby
The Ruby openssl extension was not compiled.
ERROR: Ruby install aborted due to missing extensions
Configure options used:
  --prefix=/Users/omiya/.rbenv/versions/2.3.0
  --with-readline-dir=/usr/local/opt/readline
  CC=clang
  CFLAGS= -O3 -Wno-error=shorten-64-to-32
  LDFLAGS=-L/Users/omiya/.rbenv/versions/2.3.0/lib
  CPPFLAGS=-I/Users/omiya/.rbenv/versions/2.3.0/include
  
$ CONFIGURE_OPTS="--with-openssl-dir=`brew --prefix openssl`" rbenv install 2.3.0
Downloading ruby-2.3.0.tar.bz2...
-> https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.0.tar.bz2
Installing ruby-2.3.0...
Installed ruby-2.3.0 to /Users/omiya/.rbenv/versions/2.3.0