[docs] recommend to use xenial for development

Bug: 954450
Change-Id: Ic4fbed37d692b840ef57987d2f8deaf6630054cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1689610
Auto-Submit: Takuto Ikuta <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: Takuto Ikuta <[email protected]>
Cr-Commit-Position: refs/heads/master@{#675155}
diff --git a/docs/linux_build_instructions.md b/docs/linux_build_instructions.md
index cdbcc1f..831f362a 100644
--- a/docs/linux_build_instructions.md
+++ b/docs/linux_build_instructions.md
@@ -17,7 +17,7 @@
 *   At least 100GB of free disk space.
 *   You must have Git and Python v2 installed already.
 
-Most development is done on Ubuntu (currently 14.04, Trusty Tahr). There are
+Most development is done on Ubuntu (currently 16.04, Xenial Xerus). There are
 some instructions for other distros below, but they are mostly unsupported.
 
 ## Install `depot_tools`