[12] RFR: 8209967: Bump minimum gradle version to 4.8 for JDK 11

[Kevin Rushforth]

[resend with the correct subject line]

On 8/25/2018 8:18 AM, Kevin Rushforth wrote:
> Please review the following on GitHub:
>
> https://bugs.openjdk.java.net/browse/JDK-8209967
> https://github.com/javafxports/openjdk-jfx/pull/169
>
> This bumps the minimum version of gradle for openjfx 12 to the current 
> 4.8 version (which is the version used by our builds and by gradlew). 
> This is needed in preparation for eventually bumping the minimum boot 
> JDK to 11 after JDK 11 ships.
>
> -- Kevin
>