[gegl] Update description of Exposure (more commonly used terminology + grammar match for tooltips in GIMP)

[Alexandre Prokoudine <aprokoudine src gnome org>]

commit 86ae83dfeac3b137b4ab74415da800cfedf5a03e
Author: Alexandre Prokoudine <alexandre prokoudine gmail com>
Date:   Thu Dec 28 04:56:42 2017 +0300

    Update description of Exposure (more commonly used terminology + grammar match for tooltips in GIMP)

 operations/common/exposure.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/operations/common/exposure.c b/operations/common/exposure.c
index 1d1e355..c3a6211 100644
--- a/operations/common/exposure.c
+++ b/operations/common/exposure.c
@@ -462,7 +462,7 @@ gegl_op_class_init (GeglOpClass *klass)
     "categories",  "color",
     "reference-hash", "967bd5777363d1fec59f04889f358a99",
     "reference-chain", "load path=images/standard-input.png exposure exposure=1.5",
-    "description", _("Changes Exposure of an image, allows stepping HDR and photographs up/down in stops. "),
+    "description", _("Change exposure of an image in shutter speed stops"),
     "op-version",  "1:0",
     NULL);
 }