Fix InterpolateHtmlPlugin only replacing the first occurrence

[fson]

Fixes #625 (comment).

[gaearon]

Verified on an example input?

[fson]

Verified that

    <link href="%PUBLIC_URL%/pace/theme/pace-theme-minimal.css" rel="stylesheet" />
    <script type="text/javascript">
      paceOptions = {ajax: {trackWebSockets: false}};
    </script>
    <script src="%PUBLIC_URL%/pace/pace.js"></script>

gets converted to

    <link href="/pace/theme/pace-theme-minimal.css" rel="stylesheet" />
    <script type="text/javascript">
      paceOptions = {ajax: {trackWebSockets: false}};
    </script>
    <script src="/pace/pace.js"></script>

in the HTML served by the development server.

[fson]

And checked that all occurrences of %PUBLIC_URL% get replaced with the path from homepage in the production build.

[gaearon]

Thanks