Make Suricata formula build by adding missing dep. (libmagic)

Suricata, added in #21463, fails to build with

```
checking for sechash.h... no
checking magic.h usability... no
checking magic.h presence... no
checking for magic.h... no
configure: error: magic.h not found ...
```

[The docs](https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Upgrading_Suricata_11_to_Suricata_12) show that libmagic is required. With libmagic, the formula builds successfully:

```
brew install https://raw.github.com/jm3/homebrew/master/Library/Formula/suricata.rb
######################################################################## 100.0%
==> Installing suricata dependency: libmagic
==> Downloading ftp://ftp.astron.com/pub/file/file-5.14.tar.gz
######################################################################## 100.0%
######################################################################## 100.0%==> ./configure --prefix=/usr/local/Cellar/libmagic/5.14 --enable-fsect-man5
==> make install
  /usr/local/Cellar/libmagic/5.14: 12 files, 2.7M, built in 15 seconds
==> Installing suricata
==> Downloading http://www.openinfosecfoundation.org/download/suricata-1.4.5.tar.gz
Already downloaded: /Library/Caches/Homebrew/suricata-1.4.5.tar.gz
==> ./configure --prefix=/usr/local/Cellar/suricata/1.4.5
==> make install
  /usr/local/Cellar/suricata/1.4.5: 49 files, 2.3M, built in 32 seconds
```