Convert the file libigl\include\igl\copyleft\cgal\string_to_mesh_boolean_type.cpp to UTF8-BOM to compile it with msvc2015.

Former-commit-id: c0c67eb30b0d721a4542c5ce9f501afb92d1d0d5

include/igl/copyleft/cgal/string_to_mesh_boolean_type.cpp

@@ -1,4 +1,4 @@
-#include "string_to_mesh_boolean_type.h"
+#include "string_to_mesh_boolean_type.h"
 #include <algorithm>
 #include <cassert>
 #include <vector>