v0.8.1: updated gradle build tools and gradle version

desktop/build.gradle

@@ -3,6 +3,7 @@ apply plugin: "java"
 [compileJava, compileTestJava]*.options*.encoding = 'UTF-8'
 sourceCompatibility = targetCompatibility = appJavaCompatibility
 
+ext.appMainClass = "com.shatteredpixel.shatteredpixeldungeon.desktop.DesktopLauncher"
 sourceSets.main.resources.srcDirs = [new File(project(':core').projectDir, "/src/main/assets"),
                                      new File(project(':desktop').projectDir,"/src/main/assets")]
 
@@ -15,7 +16,7 @@ task debug(dependsOn: classes, type: JavaExec) {
     classpath = sourceSets.debug.runtimeClasspath + sourceSets.main.runtimeClasspath
     ignoreExitValue = true
 
-    mainClass = "com.shatteredpixel.shatteredpixeldungeon.desktop.DesktopLauncher"
+    main = appMainClass
     systemProperty 'Specification-Title', appName
     systemProperty 'Specification-Version', appVersionName + "-INDEV"
     systemProperty 'Implementation-Version', appVersionCode
@@ -36,7 +37,7 @@ task release(dependsOn: compileForRelease, type: Jar) {
     from { configurations.runtimeClasspath.findAll { it.name.endsWith('jar') }.collect { zipTree(it) } }
 
     manifest {
-        attributes 'Main-Class': "com.shatteredpixel.shatteredpixeldungeon.desktop.DesktopLauncher"
+        attributes 'Main-Class': appMainClass
         attributes 'Specification-Title': appName
         attributes 'Specification-Version': appVersionName
         attributes 'Implementation-Version': appVersionCode