Ignore any build directory, not just 'build'

Change-Id: I958fb5d0d5cff35829b22b5d3e15e2d94356e62c
Signed-off-by: Rick Altherr <raltherr@google.com>
diff --git a/.gitignore b/.gitignore
index ccd8f51..48652c2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,3 @@
-build/*
+build*/*
 customrc
 *.sw?