Gradle Distribution Version Needs to be Updated

@thepri10 commented on [Wed May 15 2019](https://github.com/gradle-guides/building-java-9-modules/issues/37)

https://github.com/gradle-guides/building-java-9-modules/blob/24a72dc50734db670c6e5227da13ad3f12f71786/src/1-single-module/gradle/wrapper/gradle-wrapper.properties#L1

The Gradle version has to be `4.3` _or above_, otherwise `gradle run` command fails as gradle is not able to resolve `guava` dependency. The same needs to be done for each iteration of the project.

Start with src/1-single-module/gradle/wrapper/gradle-wrapper.properties at the linked line, then inspect the corresponding Gradle wrapper properties for each project iteration. Update the distribution to Gradle 4.3 or newer and verify that gradle run resolves the guava dependency successfully in each iteration.

Written by the indexing model from the issue text.