Terrific job, I would just propose some minor tweaks:
* please rename to erlang-jiffy
* please replace libstdc++-devel with gcc-c++
* please replace the git version src/jiffy.app.src with a hardcoded one:

From bcbd50f07a557865a319a161bd1471213fd681f9 Mon Sep 17 00:00:00 2001
From: Maminka <maminka.gooddata.sexy>
Date: Wed, 12 Mar 2014 09:32:04 +0100
Subject: [PATCH] set fix version

---
src/jiffy.app.src |    2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/jiffy.app.src b/src/jiffy.app.src
index 4ea304a..03cca85 100644
--- a/src/jiffy.app.src
+++ b/src/jiffy.app.src
@@ -1,6 +1,6 @@
{application, jiffy, [
    {description, "JSON Decoder/Encoder."},
-    {vsn, git},
+    {vsn, "0.8.5"},
    {registered, []},
    {applications, [kernel]}
]}.
--
1.7.1

Thank you for your kind review, sir! It's my pleasure to provide you with an improved, updated version, better than ever!

SPECS: http://v3.sk/~lkundrak/SPECS/erlang-jiffy.spec
SRPMS: http://v3.sk/~lkundrak/SRPMS/erlang-jiffy-0.8.5-2.el7.src.rpm

Almost perfect but please set the version in the patch to "0.8.5" so that is matches the package version.

SPECS: http://v3.sk/~lkundrak/SPECS/erlang-jiffy.spec
SRPMS: http://v3.sk/~lkundrak/SRPMS/erlang-jiffy-0.8.5-3.el7.src.rpm

My nipples explode with delight.

New Package SCM Request
=======================
Package Name: erlang-jiffy
Short Description: Erlang JSON parser
Owners: filabrazilska lkundrak
Branches: f19 f20 el6 epel7

Git done (by process-git-requests).

(In reply to Lubomir Rintel from comment #6)
> New Package SCM Request
> =======================
> Package Name: erlang-jiffy
> Short Description: Erlang JSON parser
> Owners: filabrazilska lkundrak
> Branches: f19 f20 el6 epel7

Lubo, could you please raise fedora-cvs again and add this address to CC list - erlang-sig ?

Package Change Request
======================
Package Name: erlang-jiffy
InitialCC: erlang-sig

Complete.