[master] eed885100 Add a hint for the UI

[Federico G. Schwindt]

commit eed885100678c4a8810c2cab2bcf1d0aa9b10d88
Author: Federico G. Schwindt <fgsch at lodoss.net>
Date:   Tue Mar 17 13:35:40 2020 +0000

    Add a hint for the UI

diff --git a/.travis.yml b/.travis.yml
index ad0b036f1..7713f3331 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -46,6 +46,7 @@ jobs:
         - ./autogen.sh
         - ./configure
     - <<: *test-linux
+      env: WITNESS=1
       script: make -j8 witness
     - <<: *test-linux
       stage: sanitizers