FindMatlab: Add support for Matlab R2015b

Modules/FindMatlab.cmake

@@ -229,6 +229,7 @@ if(NOT MATLAB_ADDITIONAL_VERSIONS)
 endif()
 
 set(MATLAB_VERSIONS_MAPPING
+  "R2015b=8.6"
   "R2015a=8.5"
   "R2014b=8.4"
   "R2014a=8.3"