extract_utils: Fix bad substitution for zsh

Change-Id: I5f4fabc62b1ac3da159b36c3ae6080e145948530
diff --git a/build/tools/extract_utils.sh b/build/tools/extract_utils.sh
index 4023208..f0a3da7 100755
--- a/build/tools/extract_utils.sh
+++ b/build/tools/extract_utils.sh
@@ -1190,7 +1190,7 @@
     local SRC="$3"
     local TARGET=
     local OAT=
-    local HOST="$(uname)"
+    local HOST="$(uname | tr '[:upper:]' '[:lower:]')"
 
     if [ -z "$BAKSMALIJAR" ] || [ -z "$SMALIJAR" ]; then
         export BAKSMALIJAR="$OMNI_ROOT"/vendor/omni/build/tools/smali/baksmali.jar