Use UTF-8 in gradle builds

common.gradle

@@ -43,6 +43,8 @@ javadoc {
     options.header = "<b>jMonkeyEngine ${jmeMainVersion} ${project.name}</b>"
     options.author = "true"
     options.use = "true"
+    options.charSet = "UTF-8"
+    options.encoding = "UTF-8"
     //disable doclint for JDK8, more quiet output
     if (JavaVersion.current().isJava8Compatible()){
         options.addStringOption('Xdoclint:none', '-quiet')

jme3-bullet/build.gradle

@@ -33,6 +33,7 @@ task generateNativeHeaders(type: Exec, dependsOn: classes) {
     args "-h", nativeIncludes
     args "@$projectDir/java_classes.jtxt"
     args '-d', classBuildDir
+    args "-encoding", "UTF-8"
 }
 
 assemble.dependsOn(generateNativeHeaders)