记得以前安装RVM还是比较简单的，现在RVM的安装过程有所变化，所以多了些麻烦。
首先还是要装git。
之后调用命令：
curl -L https://get.rvm.io | bash -s stable --ruby
但是会报这个错误：
curl: (60) SSL certificate problem, verify that the CA cert is OK. Details:
error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
More details here: http://curl.haxx.se/docs/sslcerts.html
curl performs SSL certificate verification by default, using a "bundle"
of Certificate Authority (CA) public keys (CA certs). The default
bundle is named curl-ca-bundle.crt; you can specify an alternate file
using the --cacert option.
If this HTTPS server uses a certificate signed by a CA represented in
the bundle, the certificate verification probably failed due to a
problem with the certificate (it might be expired, or the name might
not match the domain name in the URL).
If you'd like to turn off curl's verification of the certificate, use
the -k (or --insecure) option.
Could not download 'https://github.com/wayneeseguin/rvm/tarball/master'.
Make sure your certificates are up to date as described above.
To continue in insecure mode run 'echo insecure >> ~/.curlrc'.
只好根据提示调用命令：echo insecure >> ~/.curlrc
然后再执行刚才的命令，然后就可以继续执行了。
安装之后存在zlib的错误，可以参考 https://rvm.io/packages/zlib/