docs: Correct Ubuntu installation instructions

Now should work with 18.04

Change-Id: I272c76ea93e1e075f5e162f868a859f207e2804e
diff --git a/.travis.yml b/.travis.yml
index 127eddf..08e40e9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,21 +1,21 @@
 sudo: required
 language: generic
+env:
+  global:
+    - WAF_JOBS=2
 matrix:
   include:
     - os: linux
-      dist: trusty
+      dist: xenial
       env:
         - CXX=g++
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-    - os: linux
-      dist: trusty
-      env:
-        - CXX=clang++
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
+        - NODE_LABELS="Linux Ubuntu Ubuntu-16.04"
     - os: osx
+      osx_image: xcode10.1
       env:
         - CXX=clang++
-        - NODE_LABELS="OSX OSX-10.9"
+        - xcode10.1
+        - NODE_LABELS="OSX OSX_VERSION=10.13"
 notifications:
   email:
     on_success: always