[niepce] build: Exempi 2.4.x is required

[Hubert Figuière <hub src gnome org>]

commit 5159afacc6569ba2343400dead19eee20ae82f3f
Author: Hubert Figuière <hub figuiere net>
Date:   Sun Feb 11 00:45:12 2018 -0500

    build: Exempi 2.4.x is required

 README       | 2 +-
 configure.ac | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/README b/README
index ae83258..03ec784 100644
--- a/README
+++ b/README
@@ -32,7 +32,7 @@ sqlite3
 libxml2 > 2.5.0
 boost 1.60
  -boost test (for the unit test)
-exempi >= 2.2.0
+exempi >= 2.4.0
 libopenraw >= 0.1.0
 gegl >= 0.3.0
 babl
diff --git a/configure.ac b/configure.ac
index f879eeb..11ec8a8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -14,7 +14,7 @@ dnl if one is harcoded elsewhere, it is a bug
 LIBGIOMM_VERSION=2.32
 LIBGLIBMM_VERSION=2.32
 LIBGTKMM_VERSION=3.22
-EXEMPI_VERSION=2.2.0
+EXEMPI_VERSION=2.4.0
 SQLITE_VERSION=3.0
 GEGL_VERSION=0.3.0
 LIBOPENRAW_VERSION=0.1.0