Bump buidlroot version to 2018.02.6

bsp/buildroot/support/download/git

@@ -85,8 +85,11 @@ if [ ${recurse} -eq 1 ]; then
     _git submodule update --init --recursive
 fi
 
-# We do not need the .git dir; we keep other .git files, in case they
+# We do not want the .git dir; we keep other .git files, in case they
 # are the only files in their directory.
+# The .git dir would generate non reproducible tarballs as it depends on
+# the state of the remote server. It also would generate large tarballs
+# (gigabytes for some linux trees) when a full clone took place.
 rm -rf .git
 
 popd >/dev/null