Add go 1.13,1.14 to travis

.travis.yml

@@ -3,3 +3,5 @@ language: go
 go:
   - "1.8.x"
   - "1.10.x"
+  - "1.13.x"
+  - "1.14.x"

error_backward.go

@@ -2,9 +2,9 @@
 
 package errors
 
-// Is detects whether the error is equal to a given error. Errors	// Is detects whether the error is equal to a given error. Errors
-// are considered equal by this function if they are the same object,	// are considered equal by this function if they are matched by errors.Is
-// or if they both contain the same error inside an errors.Error.	// or if their contained errors are matched through errors.Is
+// Is detects whether the error is equal to a given error. Errors
+// are considered equal by this function if they are the same object,
+// or if they both contain the same error inside an errors.Error.
 func Is(e error, original error) bool {
 	if e == original {
 		return true