.travis.yml: added gcc-multilib
diff --git a/.travis.yml b/.travis.yml
index 91af96f..f2df05e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -80,6 +80,7 @@
           packages:
             - clang-3.8
             - libc6-dev-i386
+            - gcc-multilib
     - os: linux
       dist: trusty
       sudo: required