[gegl] docs: fix broken link to operation-api.html

[Øyvind Kolås <ok src gnome org>]

commit e80d109ef61c851e69d9e0ccbb4a06a8770f7732
Author: Øyvind Kolås <pippin gimp org>
Date:   Tue Sep 1 12:51:56 2015 +0200

    docs: fix broken link to operation-api.html

 docs/index.txt.in |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/docs/index.txt.in b/docs/index.txt.in
index 210890d..82949ac 100644
--- a/docs/index.txt.in
+++ b/docs/index.txt.in
@@ -30,7 +30,7 @@ link:api.html#GeglBuffer[GeglBuffer API reference]::
   GEGL contains a powerful raster buffer abstraction powered by
   link:http://gegl.org/babl/[babl].
 
-link:operations-api.html[Extending GEGL with operations/plug-ins]::
+link:operation-api.html[Extending GEGL with operations/plug-ins]::
   The API to create new image processing atoms for combination in the graph.
 link:build.html[Getting sources, and building]::
   Links and information about various ways of getting a build environment for