Large delta when only changing version number

Delta file's are 25MB in size.

This started happening about a 4 months ago and I don't think i changed anything

To reproduce download https://github.com/Mike-Wood/electron-winstaller-delta-size-test

Run: `npm install`

1. Run: `node createInstaller.js`
2. And: `node compressWin.js`

Then in the `installers/win` folder there will be an executable.

Now update the version in `package.json`

Repeat steps 1 and 2

In `installers/win` there will now be a 25MB delta file