Add Rails' CSP nonce to the script tag

[dee-see]

If a CSP is configured and enabled in development mode, it blocks the script and breaks the page. This change adds the nonce when it's configured and leaves an empty nonce tag when it isn't, which doesn't cause any issues.

[fgrehm]

Hey @dee-see , just a heads up that this is something that will come along with the upcoming 2.0 I got in the works, see the PR linked above for more.

If you have the time, it'd be great if you could give that branch a try as well, tks in advance!

[fgrehm]

Just got a pre-release ready to go. Please give that a try when you get a chance and I'll also just ping more folks for testing before a final release. This PR should auto close after code is on master.

Thanks for your contribution!

[dee-see]

Had a quick look and it seems to work well, thanks!