So this issue is still occurring on Mac when trying to download appium-1.4.13.dmg using Google Chrome
The Software versions I am using are as followed:
Google Chrome: 49.0.2623.110 (64-bit)
OSX - 10.11.3 (15D21)
As previous posts have mentioned using Firefox (v45.0.1) will allow you to successfully download the .dmg without issue.