Fix tests, which include line numbers.
--- a/ensure_test.go
+++ b/ensure_test.go
@@ -39,7 +39,7 @@
 		44.45,
 		typ{Answer: 46},
 	)
-	c.Equal(t, `ensure_test.go:41: unexpected error: foo
+	c.Equal(t, `ensure_test.go:32: unexpected error: foo
 (map[string]int) (len=1) {
  (string) (len=6) "answer": (int) 42
 }
