Add default behavior for both String and Object proxy option in package.json

[yuanalexwu]

When we fetching data from another origin we should use proxy.
Normally, we set proxy option as String in pakcage.json:

{
  "proxy": "http://abc.com"
}

It works as expected.

But, if we have several apis that are cross origin.Then we should set proxy option as an Object:

{
  "proxy": {
    "/api/foo": {
      "target": "http://abc.com" 
     },
    "/api/bar": {
      "target": "http://def.com" 
     },
   }
}

It doesn't work because of the proxy request header's host does not change the origin to the target.So we still get cross origin error

We can fix it as below:

{
  "proxy": {
    "/api/foo": {
      "target": "http://abc.com" ,
      "changeOrigin": true
     },
    "/api/bar": {
      "target": "http://def.com",
      "changeOrigin": true
     },
   }
}

I think it should be a default behavior both in String and Object proxy option

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[gaearon]

Sorry, I messed up git history. Would you mind doing

git fetch origin

Then write down hashes of your commits, do git reset --hard origin/master and cherry-pick them back onto your branch.

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[gaearon]

Can I ask you to propose these changes in #3366 and see if you can get a consensus? It's hard for me to navigate these issues, and people ask for different things about the proxy behavior. I'd like to get proxy users together so they can discuss what they need it to do.