Use relative path for cipd

Using $base_dir/cipd as a path for the cipd command only works when
$base_dir is an absolute path, not when it is a relative path, as
the current directory is already $base_dir.

Therefore, "./cipd" must be used to run a command located in $base_dir.

Change-Id: Ia882a7fb404b7ff837944f80c0ace3f4e90e6a97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4479169
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Yngve Pettersen <yngve@vivaldi.com>

bootstrap_python3

@@ -25,7 +25,7 @@ function bootstrap_python3 {
   BOOTSTRAP_PATH="bootstrap-${PYTHON3_VERSION}_bin"
 
   # Install CIPD packages. The CIPD client self-bootstraps.
-  "$base_dir/cipd" ensure -log-level warning -ensure-file "${CIPD_MANIFEST}" \
+  "./cipd" ensure -log-level warning -ensure-file "${CIPD_MANIFEST}" \
       -root "$BOOTSTRAP_PATH"
 
   BOOTSTRAP_PYTHON_BIN="${BOOTSTRAP_PATH}/python3/bin/python3"