dev-environment: Update Ubuntu version recommendation

The developent environment setup guide still suggests installing
Ubuntu 16.04, but the qemu image from CI is currently built on 18.04
and requires a newer libc (2.27 vs 2.25).

Change-Id: Ie064c542c05fbeb88b903291325add2cb6dd0e3b
Signed-off-by: Milton Miller <miltonm@us.ibm.com>
diff --git a/development/dev-environment.md b/development/dev-environment.md
index b7fc34c..a8c881c 100644
--- a/development/dev-environment.md
+++ b/development/dev-environment.md
@@ -55,10 +55,11 @@
 
 2. Install the latest Ubuntu LTS release
 
-  The majority of OpenBMC dev is on [16.04](http://releases.ubuntu.com/16.04/)
-  but whatever is most recent *should* work. The same goes for other Linux
-  distributions like Fedora but again, these are not tested nearly as much by
-  the core OpenBMC team as Ubuntu.
+  The majority of OpenBMC development community uses Ubuntu.  The qemu below
+  is built on [18.04](http://releases.ubuntu.com/18.04/) but whatever is most
+  recent *should* work. The same goes for other Linux distributions like
+  Fedora but again, these are not tested nearly as much by the core OpenBMC
+  team as Ubuntu.
 
   **VirtualBox Tips** - You'll want copy/paste working between your VM and Host.
   To do that, once you have your VM up and running: