Prevent duplicated GNU/Linux string with Trisquel's full name.

diff --git a/util/grub.d/10_linux.in b/util/grub.d/10_linux.in
index cc393be7..f13c4774 100644
--- a/util/grub.d/10_linux.in
+++ b/util/grub.d/10_linux.in
@@ -31,7 +31,14 @@ CLASS="--class gnu-linux --class gnu --class os"
 if [ "x${GRUB_DISTRIBUTOR}" = "x" ] ; then
   OS=GNU/Linux
 else
-  OS="${GRUB_DISTRIBUTOR} GNU/Linux"
+  case ${GRUB_DISTRIBUTOR} in
+      "Trisquel GNU/Linux")
+      OS="${GRUB_DISTRIBUTOR}"
+      ;;
+      *)
+      OS="${GRUB_DISTRIBUTOR} GNU/Linux"
+      ;;
+  esac
   CLASS="--class $(echo ${GRUB_DISTRIBUTOR} | tr 'A-Z' 'a-z' | cut -d' ' -f1|LC_ALL=C sed 's,[^[:alnum:]_],_,g') ${CLASS}"
 fi