Remove GWT support.

Also target source 1.9 as we no longer need 1.8 for GWT and hopefully the rest
of the world has moved on from Java 1.8 in the last twenty years.

src/test/java/com/samskivert/mustache/GwtTestMustache.java

@@ -1,23 +0,0 @@
-//
-// JMustache - A Java implementation of the Mustache templating language
-// http://github.com/samskivert/jmustache/blob/master/LICENSE
-
-package com.samskivert.mustache;
-
-import java.util.HashMap;
-import java.util.Map;
-
-import com.google.gwt.junit.client.GWTTestCase;
-
-import org.junit.*;
-import static org.junit.Assert.*;
-
-/**
- * Tests basic Mustache operation in GWT.
- */
-public class GwtTestMustache extends SharedTests
-{
-    public String getModuleName () {
-        return "com.samskivert.Mustache";
-    }
-}

src/test/java/com/samskivert/mustache/SharedTests.java

@@ -10,21 +10,16 @@ import java.io.StringReader;
 import java.io.Writer;
 import java.util.*;
 
-import com.google.gwt.junit.client.GWTTestCase;
-
 import org.junit.Test;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
 /**
- * Unit tests that can be shared between GWT and the JVM. Put GWT-only tests in
- * {@code GwtTestMustache.java} and JVM-only tests in {@code MustacheTest.java}.
+ * Vestige from when JMustache supported both GWT and JVM.
  */
-public abstract class SharedTests extends GWTTestCase
+public abstract class SharedTests
 {
-    @Override public String getModuleName () { return null; }
-
     @Test public void testSimpleVariable () {
         test("bar", "{{foo}}", context("foo", "bar"));
     }