travis: fix scons build after deprecation warning

Fixes: 54053bc8d0dad89a38e2 ("scons: Print a deprecation warning about using scons on not windows")
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
diff --git a/.travis.yml b/.travis.yml
index 23cb24f..6528b10 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -58,6 +58,6 @@
       ninja -C _build install || travis_terminate 1;
     fi
   - if test "x$BUILD" = xscons; then
-      scons || travis_terminate 1;
-      scons check || travis_terminate 1;
+      scons force_scons=1 || travis_terminate 1;
+      scons force_scons=1 check || travis_terminate 1;
     fi