Disable X11 in Chez CI bootstrap (no libx11-dev available)

ober

156bc7ccfb837e7cd8c6662236cb2bdcb1e151c4

diff --git a/.builds/ci.yml b/.builds/ci.yml
index f5e245e..35a65f0 100644
--- a/.builds/ci.yml
+++ b/.builds/ci.yml
@@ -22,7 +22,7 @@ artifacts:
 tasks:
 - build-jerboa: |
     cd jerboa
-    make jerboa
+    make jerboa CHEZ_CONFIGURE_EXTRA=--disable-x11
     echo 'export PATH="$HOME/jerboa/dist:$PATH"' >> ~/.buildenv
 - package: |
     cd jerboa-crypto