[chromecast] Add libinteraction to .gitignore

Bug: None
Test: Doesn't show up in git status
Change-Id: Ia74bba8d5c1c4df6b626784abe65d275eff8ec79
Reviewed-on: https://chromium-review.googlesource.com/1106699Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Bailey Forrest <bcf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568563}

.gitignore

@@ -205,6 +205,7 @@ vs-chromium-project.txt
 /ios/third_party/ochamcrest/src
 /ios_internal
 /libassistant
+/libinteraction
 /llvm
 /media/cast/logging/cast_logging_proto_lib.xml
 /media/cdm/api