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 6d0fb12..4a8ead3 100644
--- 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="$LINEAGE_ROOT"/prebuilts/tools-lineage/common/smali/baksmali.jar
@@ -1198,11 +1198,11 @@
     fi
 
     if [ -z "$VDEXEXTRACTOR" ]; then
-        export VDEXEXTRACTOR="$LINEAGE_ROOT"/prebuilts/tools-lineage/"${HOST,,}"-x86/bin/vdexExtractor
+        export VDEXEXTRACTOR="$LINEAGE_ROOT"/prebuilts/tools-lineage/{HOST}-x86/bin/vdexExtractor
     fi
 
     if [ -z "$CDEXCONVERTER" ]; then
-        export CDEXCONVERTER="$LINEAGE_ROOT"/prebuilts/tools-lineage/"${HOST,,}"-x86/bin/compact_dex_converter
+        export CDEXCONVERTER="$LINEAGE_ROOT"/prebuilts/tools-lineage/{HOST}-x86/bin/compact_dex_converter
     fi
 
     # Extract existing boot.oats to the temp folder