bump example version number to a safe one

stesie · stesie · commit 748256681fdd · 2018-01-06T17:13:15.000+01:00
diff --git a/README.Linux.md b/README.Linux.md
@@ -51,7 +51,7 @@ fetch v8
 cd v8
 
 # (optional) If you'd like to build a certain version:
-git checkout 5.6.326.12
+git checkout 6.4.388.18
 gclient sync
 
 # Setup GN
