Always use `open` on osx

[brigand]

Bringing this up for discussion. I don't know the rationale for the current behavior. I realize this is a bit of an edge case, and not the highest priority issue. I'll PR if there's interest.

Description

I run two instances of chrome on my computer. create-react-app is the only program that opens in the second browser instance on OSX.

To reproduce (warning, will use some HD space):

env '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome' --user-data-dir=~/.chrome-profile/foo

Leave that running, and then npm start in another terminal.

It opens in the second chrome instance.

Expected behavior

Should follow the normal OSX behavior of opening in the primary chrome instance, like open http://localhost:3000 does, or chat clients, etc.

Actual behavior

Opens in second instance.

Environment

$ npm ls react-scripts
super-counter@0.1.0 <dir>
└── react-scripts@0.9.5
$ node -v
v6.10.0
$ npm -v
3.10.10

1. Operating system: OSX
2. Browser and version: Chrome stable

[gaearon]

It happens because we try to reuse the existing tab when opening Chrome, and this is only possible with AppleScript (rather than opn). It seems that reusing existing tab is more valuable to most people than supporting running two instances of Chrome so I think this is in wontfix territory.

However you can force it to just use opn directly by passing BROWSER=open (this might work on master only).