ci: Run apt-get update before installing dependencies in travis.yml

Change-Id: I95c01ab6123c8dcec66e79207e377e1cad3355e9
diff --git a/.travis.yml b/.travis.yml
index 3f44238..f36664f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -27,6 +27,7 @@
  - NDK_BUILD_ABI=x86
  - NDK_BUILD_ABI=x86_64
 before_install:
+  - travis_retry sudo apt-get update -qq
   - travis_retry sudo apt-get install -y build-essential unzip wget pv
   - travis_retry .jenkins.d/10-get-ndk.sh
 script: