Update FindMATLAB.cmake

There are two problems with `readlink`:
1) it might give a path relative to the symlink location,
2) if matlab bin directory is in $PATH it will yield nothing.
The use of `realpath` solves both of them.

cmake/modules/FindMATLAB.cmake

@@ -93,7 +93,7 @@ else()
     IF (MATLAB_BIN_EXISTS)
       execute_process(
         COMMAND which matlab
-        COMMAND xargs readlink
+        COMMAND xargs realpath
         COMMAND xargs dirname
         COMMAND xargs dirname
         COMMAND xargs echo -n