Fix typo

Change-Id: I0635a5f4f02a1de222656133bca1ff2da8ce59f6
Reviewed-on: https://gerrit.libreoffice.org/54711Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

slideshow/opengl/rippleFragmentShader.glsl

@@ -38,7 +38,7 @@ void main()
     // We want the ripple to span all of the slide at the end of the transition.
     float t = time * (sqrt(2.0) * (slideRatio < 1.0 ? 1.0 / slideRatio : slideRatio));
 
-    // Interpolate the distance to the center in fonction of the time.
+    // Interpolate the distance to the center in function of the time.
     float mixed = smoothstep(t*w-v, t*w+v, dist);
 
     // Get the displacement offset from the current pixel, for fragments that have been touched by the ripple already.