Let's build the res zip only if needed

tools/travis-script.sh

@@ -25,12 +25,14 @@ ant update > error.txt
 cd ../..
 
 # we create resource package
+if [ "$BUILD_RES" = "YES" ]; then
     cd projects/mtg/bin/Res
     python createResourceZip.py
     # if we let the zip here, Wagic will use it in the testsuite
     # and we'll get 51 failed test cases
     mv core_*.zip ../../../../core.zip
     cd ../../../..
+fi
 
 # we're building a PSP binary here
 if [ "$BUILD_PSP" = "YES" ]; then