Installing Ruby gems on macOS

gistfile1.txt

Some gems have issues installing on macOS.
There is a list of possible solutions.


### mysql2

https://gist.github.com/fernandoaleman/ee3ac6957c2ba4f7d7d33a251d58b191

```
brew install openssl
gem install mysql2 -v '0.5.2' -- --with-ldflags=-L/usr/local/opt/openssl/lib --with-cppflags=-I/usr/local/opt/openssl/include
```


### ffi

https://github.com/ffi/ffi/issues/342#issuecomment-42968957

```
brew link libffi --force
```