CI: travis-ci: help Coverity to detect BUG_ON() as a real stop

Let's add DEBUG_STRICT=1 to coverity build definition. Hopefully,
it will resolve 1 coverity issue.
diff --git a/.travis.yml b/.travis.yml
index a8aaccb..e73d40c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -55,7 +55,7 @@
   - os: linux
     if: type == cron
     compiler: clang
-    env: TARGET=linux-glibc COVERITY_SCAN_PROJECT_NAME="Haproxy" COVERITY_SCAN_BRANCH_PATTERN="*" COVERITY_SCAN_NOTIFICATION_EMAIL="chipitsine@gmail.com" COVERITY_SCAN_BUILD_COMMAND="make CC=clang DEFINE=-DDEBUG_USE_ABORT TARGET=$TARGET $FLAGS 51DEGREES_SRC=$FIFTYONEDEGREES_SRC"
+    env: TARGET=linux-glibc COVERITY_SCAN_PROJECT_NAME="Haproxy" COVERITY_SCAN_BRANCH_PATTERN="*" COVERITY_SCAN_NOTIFICATION_EMAIL="chipitsine@gmail.com" COVERITY_SCAN_BUILD_COMMAND="make CC=clang DEFINE=-DDEBUG_USE_ABORT TARGET=$TARGET $FLAGS 51DEGREES_SRC=$FIFTYONEDEGREES_SRC DEBUG_STRICT=1"
     script:
       - |
         if [ ! -z ${COVERITY_SCAN_TOKEN+x} ]; then