[gimp-help] Fixed html link

[Marco Ciampa <marcoc src gnome org>]

commit 70cbda1efb479bd30fda69c9c367642382a2b8ff
Author: Marco Ciampa <ciampix posteo net>
Date:   Mon Jan 14 00:03:24 2019 +0100

    Fixed html link

 src/appendix/tone-mapping-tutorial.xml | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/src/appendix/tone-mapping-tutorial.xml b/src/appendix/tone-mapping-tutorial.xml
index e6984b80a..bc92720c5 100644
--- a/src/appendix/tone-mapping-tutorial.xml
+++ b/src/appendix/tone-mapping-tutorial.xml
@@ -372,8 +372,7 @@ fileref="images/tutorials/tone-mapping/gegl-exposure-mask-auto-stretched.jpg"
           after using Auto Stretch Contrast on the mask. Otherwise results 
           will be unpredictable: 
 <ulink 
-url="http://ninedegreesbelow.com/photography/unbounded-srgb-levels-gamma-slider.
-html">
+url="http://ninedegreesbelow.com/photography/unbounded-srgb-levels-gamma-slider.html";>
 Gamma adjustments produce odd results when operating on out of gamut 
 values</ulink>, 
          and Curves will summarily clip out of gamut values.