fix compiler warnings about missing end of file newlines

* added terminal newlines to some specific files which caused compiler warnings

Author: rivy

extend.cpp

@@ -310,4 +310,4 @@ namespace Sass {
     return results;
   }
 
-}
+}

subset_map.hpp

@@ -141,4 +141,4 @@ namespace Sass {
     return results;
   }
 
-}
+}

utf8_string.cpp

@@ -120,4 +120,4 @@ namespace Sass {
   }
 }
 
-#endif 
+#endif

utf8_string.hpp

@@ -32,4 +32,4 @@ namespace Sass {
   }
 }
 
-#endif 
+#endif