說明：
之前裝RVM沒有裝好，導致gem套件在安裝時都必須要加上sudo才有辦法繼續安裝。
原本不以為意，頂多安裝套件時加一下sudo就可以了。當然事情沒有這麼簡單就解決，gem有沒有加sudo安裝位置是不一樣，導致一些從網路上clone下來的程式bundle install會出現一些我無法解決的問題。
剛好今晚突然心血來潮，索性來研究一下如何安裝gem不用加上sudo。
1. 移除OSX舊有RVM
$ rvm implode
其他注意事項：
Note you may need to manually remove /etc/rvmrc and ~/.rvmrc if they exist still.
Please check all .bashrc .bash_profile .profile and .zshrc for RVM source lines and delete or comment out if this was a Per-User installation.
Also make sure to remove ‘rvm’ group if this was a system installation.
Finally it might help to relogin / restart if you want to have fresh environment (like for installing RVM again).
參考網址：RVM Implode / Uninstall and RVM Install
2. 重新安裝RVM
$ curl -L https://get.rvm.io | bash -s stable
重新啟動終端機，讓RVM生效。
其餘步驟參考網址：
註. 解決rvm use 2.0.0失敗問題
使用rvm use 2.0.0 --default出現了
RVM is not a function, selecting rubies with rvm use ... will not work.
You need to change your terminal emulator preferences to allow login shell.
Sometimes it is required to use /bin/bash --login as the command.
Please visit https://rvm.io/integration/gnome-terminal/ for a example.
解決方法：
$ subl ~/.profile
export PATH="$PATH:$HOME/.rvm/bin" # Add RVM to PATH for scripting [[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"
第二行路徑添加進去，就可以使用rvm use ..。