try apt-get update before install valgrind

cdunn2001 · cdunn2001 · commit d430756d53d7 · 2015-04-27T03:56:45.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -7,6 +7,7 @@
 # cmake is pre-installed in Travis for both linux and osx
 
 before_install:
+  - sudo apt-get update -qq
   - sudo apt-get install -qq valgrind
 os:
   - linux
