Increase default heap size to 2g

Increase default heap size to 2g

distribution/build.gradle

@@ -448,7 +448,6 @@ task run(type: RunTask) {
  * </dl>
  */
 Map<String, String> expansionsForDistribution(distributionType) {
-  String heapSize = '512m'
   String footer = "# Built for ${project.name}-${project.version} " +
       "(${distributionType})"
   Map<String, Object> expansions = [
@@ -468,8 +467,8 @@ Map<String, String> expansionsForDistribution(distributionType) {
       'def': '',
     ],
 
-    'heap.min': "${heapSize}",
-    'heap.max': "${heapSize}",
+    'heap.min': "256m",
+    'heap.max': "2g",
 
     'stopping.timeout': [
       'rpm': 86400,