Go 1.10: file_lock_test.go:43: Fatal call has possible formatting directive %s

[nim-nim]

cb568a3 does not pass unit tests with Go 1.10. At least:

Testing: "/builddir/build/BUILD/go-cb568a3e5cc06256f91a2da5a87455f717eb33f4/_build/src/github.com/siddontang/go/filelock"
+ GOPATH=/builddir/build/BUILD/go-cb568a3e5cc06256f91a2da5a87455f717eb33f4/_build:/usr/share/gocode
+ go test -buildmode pie -compiler gc -ldflags '-extldflags '\''-Wl,-z,relro  '\'''
# github.com/siddontang/go/filelock
./file_lock_test.go:43: Fatal call has possible formatting directive %s
FAIL    github.com/siddontang/go/filelock [build failed]
+ GOPATH=/builddir/build/BUILD/go-cb568a3e5cc06256f91a2da5a87455f717eb33f4/_build:/usr/share/gocode
+ go test -buildmode pie -compiler gc -ldflags '-extldflags '\''-Wl,-z,relro  '\'''
# github.com/siddontang/go/list2
./list_test.go:60: Errorf format %p has arg p of wrong type int
./list_test.go:73: Errorf format %p has arg n of wrong type int
FAIL    github.com/siddontang/go/list2 [build failed]

[siddontang]

can you send me a PR to fix it?