Update .gitignore to exclude tracked files.

.gitignore was ignoring all the files in the include/bsdiff/ directory
because the path includes "bsdiff". This fixes it to ignore only the
"bsdiff" path on the root directory.

Bug: None
Test: git ls-files -i --exclude-standard
Change-Id: Icc85d8b4b6214786cdf13b3e886e2d7240bbccdb
1 file changed