depot_tools: Fix update_depot_tools for Windows on MinGW

Bug: 1002153
Change-Id: I518073646a6c1d4e6077adf2f717008ed9972b8d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1803481Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

update_depot_tools

@@ -45,7 +45,7 @@ fi
 
 # We want to update the bundled tools even under MinGW.
 if [ $MINGW = 0 ]; then
-  $COMSPEC /c `cygpath -w "$base_dir/bootstrap/win/win_tools.bat"`
+  $COMSPEC /c `cygpath -w "$base_dir/bootstrap/win_tools.bat"`
   case $? in
     123)
       # msys environment was upgraded, need to quit.