tools/bpf: Add bootstrap/ to .gitignore

Commit 8859b0d ("tools/bpftool: Fix cross-build") added a
build-time bootstrap/ directory for bpftool, and removed
bpftool-bootstrap. Update .gitignore accordingly.

Reported-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Jean-Philippe Brucker <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: jpbrucker

tools/bpf/bpftool/.gitignore

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 *.d
-/bpftool-bootstrap
+/bootstrap/
 /bpftool
 bpftool*.8
 bpf-helpers.*