Fix build issue when build on Windows (#123)

* fix build issue when build on Windows

* proper indent

* replace with standard attribute specifier

Author: johnsonshih

pluginlib/include/pluginlib/class_loader.hpp

@@ -90,7 +90,7 @@ class ClassLoader : public ClassLoaderBase
    * \return An instance of the class
    * \deprecated use either createInstance() or createUnmanagedInstance()
    */
-  __attribute__((deprecated)) T * createClassInstance(
+  [[deprecated]] T * createClassInstance(
     const std::string & lookup_name,
     bool auto_load = true);
 

pluginlib/include/pluginlib/class_loader_imp.hpp

@@ -547,7 +547,11 @@ std::string ClassLoader<T>::getPathSeparator()
 /***************************************************************************/
 {
 #if BOOST_FILESYSTEM_VERSION >= 3
-  return boost::filesystem::path("/").native();
+#  ifdef _WIN32
+     return boost::filesystem::path("/").string();
+#  else
+     return boost::filesystem::path("/").native();
+#  endif
 #else
   return boost::filesystem::path("/").external_file_string();
 #endif