Update sw-precache-webpack-plugin to lastest version

[goldhand]

Updating sw-precache-webpack-plugin to v0.11.3 will fix the following related issues:

Windows path: #2235
Duplicate builds: #1728 (comment)

I have tested by running /bin/react-scripts.js build and asserting that the build log message is not emitted twice. The problem was discovered in this goldhand/sw-precache-webpack-plugin#78 we were calling the webpack done callback twice.

I do not have a windows machine to test the windows fix but the fix is exactly the same as in this configuration. The fix is here and has been published for a couple weeks now with no issue.

In addition to these fixes, updating to 0.11.3 will allow chunk's with hashes to be "precached" and used in importScripts.

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[gaearon]

Looks great. Thanks.