specify utf8 for gradle compiler

mcMMO-core/build.gradle

@@ -6,6 +6,7 @@ group 'com.com.gmail.com.gmail.nossr50.mcmmo'
 version '2.2.0-SNAPSHOT'
 
 sourceCompatibility = 1.8
+compileJava.options.encoding = 'UTF-8'
 
 repositories {
     
@@ -40,3 +41,4 @@ dependencies {
 
     testCompile group: 'junit', name: 'junit', version: '4.12'
 }
+