.gitignore: change path to zbootstrap.go

zbootstrap.go was moved in 1e3570ac. This updates .gitignore to match.

Change-Id: I7500e0abc8e60b6c36c6ae056b2f68b9d021fc6f
Reviewed-on: https://go-review.googlesource.com/40993
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

.gitignore

@@ -33,7 +33,7 @@ _testmain.go
 /src/cmd/cgo/zdefaultcc.go
 /src/cmd/go/internal/cfg/zdefaultcc.go
 /src/cmd/go/internal/cfg/zosarch.go
-/src/cmd/internal/obj/zbootstrap.go
+/src/cmd/internal/objabi/zbootstrap.go
 /src/go/build/zcgo.go
 /src/go/doc/headscan
 /src/runtime/internal/sys/zversion.go