Update Arch LAMP guide to replace -Sy with -Syu

pacman -Sy can cause dependency issues since it will pull repository updates but not upgrade all packages, so it can take you to a newer version of the specified package but not apply a needed upgrade for something already installed that your new package depends on.
Merge pull request #101 from akerl/patch-1

Update Arch LAMP guide to replace -Sy with -Syu