[infer][PR] Flush output after printing bugs in txt format.

Summary:
If you run `infer report --issues-txt ilovecats.txt ...` then bugs may mysteriously miss from `ilovecats.txt`, unless you flush. (See rules of thumb for `Format` module.)
Closes https://github.com/facebook/infer/pull/694

Reviewed By: mbouaziz

Differential Revision: D5442335

Pulled By: jvillard

fbshipit-source-id: 73272a0

infer/src/backend/InferPrint.ml

@@ -493,7 +493,7 @@ let pp_text_of_report fmt report =
     F.fprintf fmt "%s:%d: %s: %s %s@\n" jsonbug.file jsonbug.line jsonbug.kind jsonbug.bug_type
       jsonbug.qualifier
   in
-  List.iter ~f:pp_row report
+  List.iter ~f:pp_row report ; F.fprintf fmt "@?"
 
 module CallsCsv = struct
   (** Write proc summary stats in csv format *)