Noticed new Gradle projects have a newer structure; making changes to

reflect this. #36

build.gradle

@@ -1,3 +1,10 @@
+plugins {
+    id 'java'
+    id 'application'
+    id 'maven'
+    id 'signing'
+}
+
 repositories {
     mavenCentral()
     maven {
@@ -6,14 +13,14 @@ repositories {
     }
 }
 
-apply plugin: 'java'
-apply plugin: 'application'
-apply plugin: 'maven'
-apply plugin: 'signing'
-
 mainClassName = 'com.webcodepro.applecommander.ui.AppleCommander'
 version "${version}"
 
+compileJava {
+    sourceCompatibility = '1.8'
+    targetCompatibility = '1.8'
+}
+
 test {
     String swtDependency
     switch (System.getProperty('os.name').toLowerCase().split()[0]) {