[third_party] update .gitignore for byte_buddy

For
https://chromium-review.googlesource.com/c/chromium/src/+/1755125

Bug: 876922
Change-Id: I944eb771d41b4aa93db271a58eff025139d64aea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1757956
Commit-Queue: John Budorick <jbudorick@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688288}

third_party/.gitignore

@@ -44,6 +44,7 @@
 /boringssl/src
 /bouncycastle/lib/
 /breakpad/breakpad
+/byte_buddy/android_sdk_build_tools_25_0_2
 /byte_buddy/lib/
 /cacheinvalidation/cacheinvalidation_unittests_run.xml
 /cardboard-java/src