Make buildscripts backwards compatible with Gradle 4.0

.travis.yml

@@ -1,6 +1,8 @@
 language: java
 jdk:
   - oraclejdk8
+before_install:
+  - gradle wrapper
 before_cache:
   - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
   - rm -fr $HOME/.gradle/caches/*/plugin-resolution/

cache/build.gradle

@@ -1,6 +1,4 @@
-plugins {
-    id "java-library"
-}
+apply plugin: 'java-library'
 
 description = 'Apollo Cache'
 

game/build.gradle

@@ -1,8 +1,6 @@
-plugins {
-    id 'application'
-    id 'org.jetbrains.kotlin.jvm'
-    id 'org.jetbrains.kotlin.plugin.scripting'
-}
+apply plugin: 'application'
+apply plugin: 'org.jetbrains.kotlin.jvm'
+apply plugin: 'org.jetbrains.kotlin.plugin.scripting'
 
 description = 'Apollo Game'
 mainClassName = 'org.apollo.Server'

game/plugin-testing/build.gradle

@@ -1,7 +1,5 @@
-plugins {
-    id 'java-library'
-    id 'org.jetbrains.kotlin.jvm'
-}
+apply plugin: 'java-library'
+apply plugin: 'org.jetbrains.kotlin.jvm'
 
 dependencies {
     api project(':game')

net/build.gradle

@@ -1,6 +1,4 @@
-plugins {
-    id 'java-library'
-}
+apply plugin: 'java-library'
 
 description = 'Apollo Net'
 

util/build.gradle

@@ -1,6 +1,4 @@
-plugins {
-    id "java-library"
-}
+apply plugin: 'java-library'
 
 description = 'Apollo Utilities'