Add use strict to generate-sw for Node 4 support

[MaxLeiter]

R: @jeffposnick @addyosmani @gauntface

Fixes #670

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[MaxLeiter]

Signed

[googlebot]

CLAs look good, thanks!

[jeffposnick]

Thanks for the contribution, @MaxLeiter!

I'd like to move the discussion to #669 in lieu of merging this PR as-is. I know that there are other files inside of workbox-build that are using const and let, so I have a feeling that the change in this PR wouldn't be sufficient. We should talk about addressing it in a more holistic fashion.

[MaxLeiter]

Should be good to go. Ping @jeffposnick

[gauntface]

Was looking into adding testing for node 4 but it's going to be a pretty big headache since selenium doesn't support anything lower than node 6.

@jeffposnick I'm fine with taking this PR, any other comments from you?

[jeffposnick]

👍

[MaxLeiter]

any chance of a 1.1.1 release?

[jeffposnick]

It's in https://github.com/GoogleChrome/workbox/releases/tag/v1.2.0