Typo in Mac OS X section of Helm install guide

[Ben Hamilton]

There's a small but important typo in the Mac OS X section of the Helm install guide at:

http://helm-engine.org/guide/installing/

$ brew install cairo --without-x

$ brew install pango --without-x

should be:

$ brew install cairo --without-x11

$ brew install pango --without-x11

The former doesn't actually avoid the X11 dependency, and asks you to install XQuartz:

$ brew install cairo --without-x

cairo: Unsatisfied dependency: XQuartz 0.0.0

Homebrew does not package XQuartz. Installers may be found at:

  https://xquartz.macosforge.org

Error: An unsatisfied requirement failed this build.