errors.go: "nor" -> "not" (typo fix) (#17)
diff --git a/errors.go b/errors.go
index 7ec1c5d..b0da7c5 100644
--- a/errors.go
+++ b/errors.go
@@ -36,7 +36,7 @@
 //     }
 //
 // can be inspected by errors.Cause. errors.Cause will recursively retrieve
-// the topmost error which does nor implement causer, which is assumed to be
+// the topmost error which does not implement causer, which is assumed to be
 // the original cause. For example:
 //
 //     switch err := errors.Cause(err).(type) {