Cover failing tests

The previous test suite only included passing tests.  We want to cover
failing tests too.

Author: mndrix

util/tap/Makefile

@@ -1,4 +1,4 @@
-TESTS = auto check known writer
+TESTS = auto check known failing writer
 GOPATH = $(CURDIR)/gopath
 
 .PHONY: $(TESTS)

util/tap/test/failing/main.go

@@ -0,0 +1,9 @@
+package main
+
+import "github.com/mndrix/tap-go"
+
+func main() {
+	t := tap.New()
+	t.Header(1)
+	t.Ok(false, "first test")
+}