go/printer: update golden file (fix build)

Change-Id: I897a09a1c54f6d68c5dc68e189cb25dc72bb7590
Reviewed-on: https://go-review.googlesource.com/3240Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/printer/testdata/declarations.golden

@@ -111,6 +111,9 @@ import (
 )
 
 // print import paths as double-quoted strings
+// (we would like more test cases but the go/parser
+// already excludes most incorrect paths, and we don't
+// bother setting up test-ASTs manually)
 import (
 	"fmt"
 	"math"