Moves to official vendoring solution

vendor/github.com/onsi/gomega/matchers/be_nil_matcher.go

@@ -0,0 +1,18 @@
+package matchers
+
+import "github.com/onsi/gomega/format"
+
+type BeNilMatcher struct {
+}
+
+func (matcher *BeNilMatcher) Match(actual interface{}) (success bool, err error) {
+	return isNil(actual), nil
+}
+
+func (matcher *BeNilMatcher) FailureMessage(actual interface{}) (message string) {
+	return format.Message(actual, "to be nil")
+}
+
+func (matcher *BeNilMatcher) NegatedFailureMessage(actual interface{}) (message string) {
+	return format.Message(actual, "not to be nil")
+}