Delete pre_build hook of docker hub

hooks/pre_build

@@ -1,12 +0,0 @@
-#!/bin/bash
-
-./gradlew clean build -x test
-
-echo "=> Building the binary"
-docker run \
-  -v $(pwd):/src \
-  -v /var/run/docker.sock:/var/run/docker.sock \
-  -w="/src" \
-  openjdk:8-jdk-alpine \
-  ./gradlew clean build -x test
-echo "=> Built the binary successfully"