Increase Java VM maximum heap size to 1024MB 

I got "java.lang.OutOfMemoryError: Java heap space" error when I'm building own Kang (galaxys2 for example) with Gapps included.
Increase maximum heap size to 1024MB will solve it.
diff --git a/tools/squisher b/tools/squisher
index ce5e916..c6640c5 100755
--- a/tools/squisher
+++ b/tools/squisher
@@ -155,7 +155,7 @@
 echo
 printf "Signing package..."
 SECURITYDIR=$ANDROID_BUILD_TOP/build/target/product/security
-java -Xmx512m \
+java -Xmx1024m \
 	-jar $ANDROID_BUILD_TOP/out/host/$OUT_TARGET_HOST/framework/signapk.jar \
 	-w $SECURITYDIR/testkey.x509.pem $SECURITYDIR/testkey.pk8 \
 	$REPACK/update.zip $OUTFILE