Add note to doc

dependencies.md

@@ -3,12 +3,14 @@
 To ensure the broadest compatibility when building the benchmark library, but
 still allow forward progress, we require any build tooling to be available for:
 
+* Debian stable AND
 * The last two Ubuntu LTS releases AND
-* Debian stable
 
 Currently, this means using build tool versions that are available for Ubuntu
 16.04 (Xenial), Ubuntu 18.04 (Bionic), and Debian stretch.
 
+_Note, [travis](.travis.yml) runs under Ubuntu 14.04 (Trusty) for linux builds._
+
 ## cmake
 The current supported version is cmake 3.5.1 as of 2018-06-06.