Fix windows build

[ExE-Boss]

Fixes the \r symbol remaining at the end of entry in the file utils/update-flash-refs.js:194, which resulted in the build not working on Windows.

[ivanpopelyshev]

That's not the only problem in windows build, see https://github.com/mozilla/shumway/pull/2442/files
The best way is just to specify list of files with strict LF

[ExE-Boss]

That \r is put there by the Windows filesystem regardless of the value of eol in .gitconfig, so this patch is still also necessary (this only fixes the extension build).

[ivanpopelyshev]

The idea is that you cant fix the code for xargs in the mozilla-build, so I have to add certain file in ".gitattributes" and prevent git-for-windows auto-CLRF mechanism.

There are many ways to fix that, I made a comment only to get your interest in the project again. Why did you try to build it?

[ExE-Boss]

I tried to build it because I’m working on #2435.

Also, the purpose of this PR is just to make it possible for grunt firefox or any other grunt build command to complete successfully on Windows without needing to use WSL.