leg-java: bump image size to 3GB

Accommodating the jtreg tests.

Signed-off-by: Andrew McDermott <andrew.mcdermott@linaro.org>
diff --git a/build_images.py b/build_images.py
index b9386d3..08e56a2 100755
--- a/build_images.py
+++ b/build_images.py
@@ -79,7 +79,7 @@
     'alip': '2G',
     'developer': '1G',
     'lamp-armv8': '2G',
-    'leg-java-armv8': '2G',
+    'leg-java-armv8': '4G',
     'linarotv-xbmc': '3G',
     'minimal-armv8': '512M',
     'nano': '1G',