MINOR: Update minimum required Gradle version to 4.7 (#5642)
MINOR: Update minimum required Gradle version to 4.7 (#5642)

After commit f123d2f, the minimum required gradle version changed to 4.7

This is due to the use of isJava11Compatible() in build.gradle. It was
introduced in version 4.7 (https://github.com/gradle/gradle/blob/master/subprojects/base-services/src/main/java/org/gradle/api/JavaVersion.java#L172-L180)

Reviewers: Ismael Juma <0794a5c7e497910d682bf2c54c66cc30760c0221@juma.me.uk>
sslavic/kafka,KevinLiLu/kafka,Chasego/kafka,TiVo/kafka,gf53520/kafka,TiVo/kafka,sslavic/kafka,gf53520/kafka,KevinLiLu/kafka,sslavic/kafka,lindong28/kafka,TiVo/kafka,noslowerdna/kafka,guozhangwang/kafka,Chasego/kafka,Chasego/kafka,lindong28/kafka,KevinLiLu/kafka,mihbor/kafka,guozhangwang/kafka,guozhangwang/kafka,apache/kafka,KevinLiLu/kafka,gf53520/kafka,noslowerdna/kafka,guozhangwang/kafka,mihbor/kafka,Chasego/kafka,sslavic/kafka,noslowerdna/kafka,mihbor/kafka,lindong28/kafka,gf53520/kafka,lindong28/kafka,noslowerdna/kafka,apache/kafka,apache/kafka,mihbor/kafka,TiVo/kafka,apache/kafka