fix typo

build.sh

@@ -84,7 +84,7 @@ function fail {
   # construct a Info.plist
   sed -f <(echo "${info_plist_replacements}") files/Info.plist > ${work_dir}/${app_bundle_name}/Contents/Info.plist || fail
   # copy README
-  cp files/README.txt "${workdir}" || fail
+  cp files/README.txt "${work_dir}" || fail
 
   # create disk image
   genisoimage -quiet -V "${app_name}-${app_version}" -D -R -apple -no-pad -o "${app_name}-${app_version}.dmg" "${work_dir}" || fail