CI: use address sanitizer

[Akim Demaille]

commit c85418ba07fd56230b11ae0579681d1735e4f9aa
Author: Akim Demaille <address@hidden>
Date:   Mon Sep 10 06:35:53 2018 +0200

    CI: use address sanitizer
    
    * .travis.yml (matrix): Use the latest (available) clang with asan.

diff --git a/.travis.yml b/.travis.yml
index c228c63f..debb3f0b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -78,6 +78,16 @@ matrix:
       env:
         - MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0 && CPPFLAGS=-DNDEBUG && 
CFLAGS=-O3 && CXXFLAGS=-O3"
 
+    - os: linux
+      addons:
+        apt:
+          sources:
+            - llvm-toolchain-trusty-5.0
+          packages:
+            - clang-5.0
+      env:
+        - MATRIX_EVAL="CC='clang-5.0 -fsanitize=address' && CXX='clang++-5.0 
-fsanitize=address'"
+
     - os: linux
       addons:
         apt: