Update changelog

debian/changelog

+libshadertoy (0.1.6) unstable; urgency=medium
+
+  * Add fragment shader execution time query support (iTimeDelta)
+  * Fix unsupported inputs in examples
+  * Fix mipmap generation
+  * Fix version parsing for source build
+
+ -- Vincent Tavernier <vincent.tavernier@inria.fr>  Thu, 08 Feb 2018 11:30:00 +0200
+
 libshadertoy (0.1.5) unstable; urgency=medium
 
   * Update dependencies for Xenial and Stretch